Initial checkin for stack protectors. Here's what it does:

* The prologue is modified to read the __stack_chk_guard global and insert it
onto the stack.

* The epilogue is modified to read the sto

Initial checkin for stack protectors. Here's what it does:

* The prologue is modified to read the __stack_chk_guard global and insert it
onto the stack.

* The epilogue is modified to read the stored guard from the stack and compare
it to the original __stack_chk_guard value. If they differ, then the
__stack_chk_fail() function is called.

* The stack protector needs to be first on the stack (after the parameters) to
catch any stack-smashing activities.

Front-end support will follow after a round of beta testing.

llvm-svn: 58673

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