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.
#53811

(cherry picked from commit 52fc796)

src/codegen.cpp

@@ -6679,6 +6679,7 @@ static jl_cgval_t emit_cfunction(jl_codectx_t &ctx, jl_value_t *output_type, con
     if (ctx.emission_context.TargetTriple.isAArch64() || ctx.emission_context.TargetTriple.isARM() || ctx.emission_context.TargetTriple.isPPC64()) {
         if (nest) {
             emit_error(ctx, "cfunction: closures are not supported on this platform");
+            JL_GC_POP();
             return jl_cgval_t();
         }
     }