Improve support for completely unknown architectures (#10107)

* Improve support for completely unknown architectures

This commit is a step in the direction of trying to make Wasmtime more
portable

Improve support for completely unknown architectures (#10107)

* Improve support for completely unknown architectures

This commit is a step in the direction of trying to make Wasmtime more
portable by default. The goal here is to enable Wasmtime to compile for
architectures that it has no prior knowledge of. There's a few
miscellaneous locations through Wasmtime where we need
architecture-specific intrinsics and such but that's all in service of
Cranelift itself. Without Cranelift support none of them are necessary.

This commit plumbs a custom `#[cfg]` from Wasmtime's `build.rs` script
into the crate about whether there's a supported Cranelift backend. If
this isn't available some architecture-specific intrinsics are turned
off and not included. An example is that `vm::arch` entirely disappears
which is only in service of `UnwindHost`, which also disappears.
Furthermore the `helpers.c` file also entirely disappears as it's not
necessary on unknown architectures.

To help keep this working I've added CI to build Wasmtime for
`powerpc64le-unknown-linux-gnu`. Wasmtime currently has no support for
this architecture, although if it grows such support in the future
this'll need to be changed to some other unsupported architecture.

* Review feedback

* Fix powerpc build

* Refactor windows trap handling to look like Unix

Shuffle some files around to be more amenable to #[cfg]

* Move signal-handling tests to wasmtime crate

That way it's got easy access to the #[cfg]'s from the build script

* Disable signals support without a host compiler

Even if custom signals are enabled, don't compile it in.

prtest:full

* Fix windows unused imports

* Fix unused imports on Windows

* Remove untested stubs for arch intrinsics

These aren't needed any more to compile Pulley

* Defer tunables validation to loading modules

Instead of validating at `Engine` config time instead validate at
`Module` config time to enable cross-compilation.

* Skip `Tunables` auto-configuration if cross-compiling

This commit

* Tweak some Tunables based on Pulley

Ensures that specific `--target pulleyNN` works most of the time.

* Update host_segfault.rs to handle new 32-bit defaults

No signal handlers are used at all with Pulley so when the async stack
overflows there's no message printed any more.

* Disable Tunables::signals_based_traps on miri

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Replace `signals-based-traps` with auto-detection (#9941)

* Replace `signals-based-traps` with auto-detection

This commit refactors the platform support of the `wasmtime` crate
itself to remove the

Replace `signals-based-traps` with auto-detection (#9941)

* Replace `signals-based-traps` with auto-detection

This commit refactors the platform support of the `wasmtime` crate
itself to remove the previously added `signals-based-traps` feature in
favor of auto-detecting whether it's there or not. The `build.rs`
script for the `wasmtime` crate will now detect the target platform and
auto-enable this feature as necessary.

The `signals-based-traps` cargo feature is removed and split into two
custom `#[cfg]` directives that the build script sets:

* `has_virtual_memory` - this is used to gate mmap implementations for
example. This is enabled on `unix || windows` and will be off for
`no_std` targets for example. This is split out of
"signals-based-traps" to better handle platforms like iOS which have
virtual memory but don't execute native code (removing the need for
native signals).

* `has_native_signals` - gates signal handlers on Unix for example. This
is disabled on MIRI but otherwise enabled for `unix || windows`. This
is intended to in the future get disabled for iOS by default for
example since it's not necessary when using Pulley. This is
additionally off-by-default for `no_std` platforms.

Two new crate features were added for `no_std` or "custom" platforms to
opt-in to the `wasmtime-platform.h` C APIs for implementing virtual
memory and signals. These are used in the `min-platform` embedding example.

This commit additionally updates some various documentation here and
there to be more up-to-date.

* Update CI configuration

* Fix compile warnings

* Fix test on miri

* Fix more tests on miri

* Fix some warnings

* Another round of miri/CI attempts/fixes

prtest:full

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Fix build on 32-bit Windows; consolidate CI platform checks (#9883)

* Fix build on 32-bit Windows; consolidate CI platform checks

This commit fixes the build of the `wasmtime` crate and CLI on 32-b

Fix build on 32-bit Windows; consolidate CI platform checks (#9883)

* Fix build on 32-bit Windows; consolidate CI platform checks

This commit fixes the build of the `wasmtime` crate and CLI on 32-bit
Windows. This required adding some extra bits for trap handling and a
stub for "unimplemented" for unwind information registration. This then
additionally refactored our CI configuration to place all of the
cross-compile checks in one matrix instead of spread out across a few
jobs.

Closes #9882

prtest:platform-checks

* Add "join" node in CI

* Who really knows yml syntax

* Remove dead checks

* Fix only-`runtime` build on Windows

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Add support for `#![no_std]` to the `wasmtime` crate (#8533)

* Always fall back to custom platform for Wasmtime

This commit updates Wasmtime's platform support to no longer require an
opt-in `RUSTF

Add support for `#![no_std]` to the `wasmtime` crate (#8533)

* Always fall back to custom platform for Wasmtime

This commit updates Wasmtime's platform support to no longer require an
opt-in `RUSTFLAGS` `--cfg` flag to be specified. With `no_std` becoming
officially supported this should provide a better onboarding experience
where the fallback custom platform is used. This will cause linker
errors if the symbols aren't implemented and searching/googling should
lead back to our docs/repo (eventually, hopefully).

* Change Wasmtime's TLS state to a single pointer

This commit updates the management of TLS to rely on just a single
pointer rather than a pair of a pointer and a `bool`. Additionally
management of the TLS state is pushed into platform-specific modules to
enable different means of managing it, namely the "custom" platform now
has a C function required to implement TLS state for Wasmtime.

* Delay conversion to `Instant` in atomic intrinsics

The `Duration` type is available in `no_std` but the `Instant` type is
not. The intention is to only support the `threads` proposal if `std` is
active but to assist with this split push the `Duration` further into
Wasmtime to avoid using a type that can't be mentioned in `no_std`.

* Gate more parts of Wasmtime on the `profiling` feature

Move `serde_json` to an optional dependency and gate the guest profiler
entirely on the `profiling` feature.

* Refactor conversion to `anyhow::Error` in `wasmtime-environ`

Have a dedicated trait for consuming `self` in addition to a
`Result`-friendly trait.

* Gate `gimli` in Wasmtime on `addr2line`

Cut down the dependency list if `addr2line` isn't enabled since then
the dependency is not used. While here additionally lift the version
requirement for `addr2line` up to the workspace level.

* Update `bindgen!` to have `no_std`-compatible output

Pull most types from Wasmtime's `__internal` module as the source of
truth.

* Use an `Option` for `gc_store` instead of `OnceCell`

No need for synchronization here when mutability is already available in
the necessary contexts.

* Enable embedder-defined host feature detection

* Add `#![no_std]` support to the `wasmtime` crate

This commit enables compiling the `runtime`, `gc`, and `component-model`
features of the `wasmtime` crate on targets that do not have `std`. This
tags the crate as `#![no_std]` and then updates everything internally to
import from `core` or `alloc` and adapt for the various idioms. This
ended up requiring some relatively extensive changes, but nothing too
too bad in the grand scheme of things.

* Require `std` for the perfmap profiling agent

prtest:full

* Fix build on wasm

* Fix windows build

* Remove unused import

* Fix Windows/Unix build without `std` feature

* Fix some doc links

* Remove unused import

* Fix build of wasi-common in isolation

* Fix no_std build on macos

* Re-fix build

* Fix standalone build of wasmtime-cli-flags

* Resolve a merge conflict

* Review comments

* Remove unused import

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Turn the `wasmtime-runtime` crate into the `wasmtime::runtime::vm` module (#8501)

* Expose `wasmtime-runtime` as `crate::runtime::vm` internally for the `wasmtime` crate

* Rewrite uses of `wasmtime

Turn the `wasmtime-runtime` crate into the `wasmtime::runtime::vm` module (#8501)

* Expose `wasmtime-runtime` as `crate::runtime::vm` internally for the `wasmtime` crate

* Rewrite uses of `wasmtime_runtime` to `crate::runtime::vm`

* Remove dep on `wasmtime-runtime` from `wasmtime-cli`

* Move the `wasmtime-runtime` crate into the `wasmtime::runtime::vm` module

* Update labeler for merged crates

* Fix `publish verify`

prtest:full

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