libsa: Remove conflicting .global/.weak directive

LLVM12 complains if you change the symbol binding:
`error: _longjmp changed binding to STB_GLOBAL`
In this case LLVM actually ignored the weak direc

libsa: Remove conflicting .global/.weak directive

LLVM12 complains if you change the symbol binding:
`error: _longjmp changed binding to STB_GLOBAL`
In this case LLVM actually ignored the weak directive and used the
later .global, but GNU as would mark the symbol as weak.
None of the other architectures mark the libsa _setjmp as weak so
just drop this directive.

(cherry picked from commit 59b2caef0537661397caf2ce1398cf802cb864b4)

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