Cherry-pick: [builtins] Move cfi start's after the symbol name [NFC]

[tmandry]

... in preparation for diagnosing improperly nested .cfi regions.

See https://reviews.llvm.org/D155245

---

This cherry-pick of 7939ce3 fixes an issue when building compiler-builtins with clang from LLVM main. The check in the linked diff / commit d506aa4 rejects the assembly due to improperly nested CFI regions:

  running: env -u IPHONEOS_DEPLOYMENT_TARGET "/Volumes/Work/s/w/ir/x/w/cipd/bin/clang" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-gdwarf-2" "-fno-omit-frame-pointer" "--target=arm64-apple-darwin" "-ffunction-sections" "-fdata-sections" "-fPIC" "--target=arm64-apple-darwin" "--target=aarch64-apple-darwin" "--sysroot=/Volumes/Work/s/w/ir/cache/macos_sdk/XCode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk" "-mno-outline-atomics" "-I" "/Volumes/Work/s/w/ir/x/w/fuchsia-third_party-rust/src/llvm-project/compiler-rt/lib/builtins" "-fno-builtin" "-fvisibility=hidden" "-ffreestanding" "-fomit-frame-pointer" "-ffile-prefix-map=/Volumes/Work/s/w/ir/x/w/fuchsia-third_party-rust/src/llvm-project/compiler-rt=." "-DVISIBILITY_HIDDEN" "-o" "/Volumes/Work/s/w/ir/x/w/staging/build/fuchsia-build/x86_64-apple-darwin/stage2-std/aarch64-apple-darwin/release/build/compiler_builtins-d4c39d93f1fd5499/out/657ee1fe8a0b7177-lse_cas1_relax.o" "-c" "/Volumes/Work/s/w/ir/x/w/staging/build/fuchsia-build/x86_64-apple-darwin/stage2-std/aarch64-apple-darwin/release/build/compiler_builtins-d4c39d93f1fd5499/out/lse_cas1_relax.S"
  cargo:warning=/Volumes/Work/s/w/ir/x/w/fuchsia-third_party-rust/src/llvm-project/compiler-rt/lib/builtins/aarch64/lse.S:145:120: error: non-private labels cannot appear between .cfi_startproc / .cfi_endproc pairs
  cargo:warning= .text %% .balign 16 %% .globl __aarch64_cas1_relax %% %% .private_extern __aarch64_cas1_relax %% %% .cfi_startproc %% __aarch64_cas1_relax: %%
  cargo:warning=                                                                                                                       ^
  cargo:warning=/Volumes/Work/s/w/ir/x/w/fuchsia-third_party-rust/src/llvm-project/compiler-rt/lib/builtins/aarch64/lse.S:145:102: error: previous .cfi_startproc was here
  cargo:warning= .text %% .balign 16 %% .globl __aarch64_cas1_relax %% %% .private_extern __aarch64_cas1_relax %% %% .cfi_startproc %% __aarch64_cas1_relax: %%
  cargo:warning=                                                                                                     ^
  exit status: 1

[nikic]

Do I understand correctly that you are using clang from main, but not building rustc against main?

[tmandry]

Yes, we update our clang every few weeks from main, but build Rust with its canonical LLVM pin for now.