SIGSEGV/SIGILL while building `rustc` itself in x86_64 apple CI jobs

This does not seem like an isolated case, see label https://github.com/rust-lang/rust/labels/CI-spurious-x86_64-apple-SIGSEGV-SIGILL

In the revert PR #134207, non-compiler (and AFAICT unrelated changes) ran into a SIGSEGV while compiling rustc_codegen_llvm on the dist-x86_64-apple job.

CI job: https://github.com/rust-lang-ci/rust/actions/runs/12298794250/job/34323085670
Log: https://github.com/rust-lang/rust/pull/134207#issuecomment-2539381085

  [RUSTC-TIMING] rustc_codegen_llvm test:false 62.093
  rustc exited with signal: 11 (SIGSEGV)
  error: could not compile `rustc_codegen_llvm` (lib)
  
  Caused by:
    process didn't exit successfully: `/Users/runner/work/rust/rust/build/bootstrap/debug/rustc /Users/runner/work/rust/rust/build/bootstrap/debug/rustc --crate-name rustc_codegen_llvm --edition=2021 compiler/rustc_codegen_llvm/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no -C codegen-units=1 --check-cfg 'cfg(docsrs)' --check-cfg 'cfg(feature, values())' -C metadata=31812fcdce1ed1a6 -C extra-filename=-31812fcdce1ed1a6 --out-dir /Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps --target x86_64-apple-darwin -L dependency=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps -L dependency=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/release/deps --extern bitflags=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libbitflags-a1ecb01bec05c607.rmeta --extern itertools=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libitertools-fc8482292e402829.rmeta --extern libc=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/liblibc-71418dd2bae71546.rmeta --extern measureme=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libmeasureme-65f26e237d9cbc69.rmeta --extern object=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libobject-b9fdd0c4eec82855.rmeta --extern rustc_demangle=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_demangle-59d4195c10f8ce59.rmeta --extern rustc_abi=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_abi-8c308e15a91667ae.rmeta --extern rustc_ast=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_ast-6307ddaffbb78c2c.rmeta --extern rustc_attr=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_attr-a64f29895039e85d.rmeta --extern rustc_codegen_ssa=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_codegen_ssa-471fc4cdea12e5aa.rmeta --extern rustc_data_structures=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_data_structures-ad6787aabac41fc7.rmeta --extern rustc_errors=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_errors-ae10afa2bd2798f4.rmeta --extern rustc_fluent_macro=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/release/deps/librustc_fluent_macro-e27f644eab9503e4.dylib --extern rustc_fs_util=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_fs_util-1af14c49c485068e.rmeta --extern rustc_hir=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_hir-ddd2bd35821eba08.rmeta --extern rustc_index=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_index-ba2f5cf42e80b6b3.rmeta --extern rustc_llvm=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_llvm-a806c45190fb0592.rmeta --extern rustc_macros=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/release/deps/librustc_macros-21f9064df7350bce.dylib --extern rustc_metadata=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_metadata-8c77a936e16e5034.rmeta --extern rustc_middle=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_middle-8709a3bcf14547b0.rmeta --extern rustc_query_system=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_query_system-531ae3841194b38a.rmeta --extern rustc_sanitizers=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_sanitizers-21a20f1a3f01e840.rmeta --extern rustc_session=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_session-63c14fae59e29aee.rmeta --extern rustc_span=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_span-2d8da5b611828dda.rmeta --extern rustc_symbol_mangling=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_symbol_mangling-595e7538c1ed6229.rmeta --extern rustc_target=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/librustc_target-bcb3e09908ca7102.rmeta --extern serde=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libserde-632f5b42d8037b7d.rmeta --extern serde_json=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libserde_json-b239b225d337f1f5.rmeta --extern smallvec=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libsmallvec-e8983336671b9a36.rmeta --extern tracing=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/deps/libtracing-6a46015c9b81a7be.rmeta --cfg=windows_raw_dylib -Csymbol-mangling-version=v0 -Zunstable-options '--check-cfg=cfg(bootstrap)' '--check-cfg=cfg(llvm_enzyme)' -Zmacro-backtrace -Csplit-debuginfo=unpacked '-Wrustc::internal' '-Drustc::symbol_intern_string_literal' -Wkeyword_idents_2024 -Wunsafe_op_in_unsafe_fn -Zosx-rpath-install-name '-Clink-args=-Wl,-rpath,@loader_path/../lib' -Zon-broken-pipe=kill -Zdylib-lto -Clto=thin -Cembed-bitcode=yes -Z binary-dep-depinfo -L native=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/build/psm-c80cca6b00966791/out -L native=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/build/blake3-dcfcf6f77ce37e35/out -L native=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/build/blake3-dcfcf6f77ce37e35/out -L native=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage1-rustc/x86_64-apple-darwin/release/build/rustc_llvm-d5c0fad7751ae19c/out -L native=/Users/runner/work/rust/rust/build/x86_64-apple-darwin/llvm/lib` (exit status: 254)
  warning: build failed, waiting for other jobs to finish...
  [RUSTC-TIMING] rustc_hir_analysis test:false 291.587

Unfortunately, I don't have a repro or details, and it might be spurious (which is still not good). Opening to record in case anyone else also run into this, and that this might be a genuine issue (like a miscompile or whatever).

Start with the referenced dist-x86_64-apple CI job and its log, then inspect compiler/rustc_codegen_llvm/src/lib.rs and the reported rustc build command. The issue has no reproduction or specified code change; progress would require identifying whether the SIGSEGV/SIGILL is reproducible and documenting a cause, fix, or mitigation.