Add missing GC_POP() in emit_cfunction (#53809)
~~Apparently somewhere in codegen inside `emit_codeinst`some piece of
code is relying on the implicit try catch gcstack restoring. I haven't
got the analyzer working on that file yet (it has hundreds of issues and
it doesn't like C++ code that much + the file is tens of thousands of
lines after includes so it struggles).~~
This fixes the compileall segfault in apple-aarch64 ci.
https://github.com/JuliaLang/julia/issues/53811
