Fix trampoline assembly for build on clang 18 on apple silicon (#54634)
This avoids a: `error: non-private labels cannot appear between
.cfi_startproc / .cfi_endproc pairs` error.
That error was introduced in https://reviews.llvm.org/D155245#4657075
see also https://github.com/llvm/llvm-project/issues/72802