Classify .s files as AssemblerToPreprocess so #include/#ifdef are honored

[sylvestre]

a previous change broke firefox with:

[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  gmake[4]: Entering directory '/builds/worker/workspace/obj-build/security'
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  /builds/worker/fetches/sccache/sccache /builds/worker/fetches/clang/bin/clang -isysroot /builds/worker/fetches/MacOSX26.4.sdk -mmacosx-version-min=10.15 --target=x86_64-apple-darwin -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fstack-protector-strong -fstrict-flex-arrays=1 -pthread -ffunction-sections -fdata-sections -fno-math-errno -fPIC -fcrash-diagnostics-dir=/builds/worker/artifacts -gdwarf-4 -gsimple-template-names -Xclang -load -Xclang /builds/worker/workspace/obj-build/build/clang-plugin/libclang-plugin.so -Xclang -add-plugin -Xclang moz-check -O3 -fno-omit-frame-pointer -funwind-tables -Werror  -o ../dist/bin/libnss3.dylib -Wl,@/builds/worker/workspace/obj-build/security/libnss3_dylib.list    -fuse-ld=lld -fstack-protector-strong -Wl,-dead_strip   ../dist/bin/libmozglue.dylib -Wl,-exported_symbols_list,libnss3.dylib.symbols -dynamiclib -install_name @rpath/libnss3.dylib -compatibility_version 1 -current_version 1  -framework CoreServices
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  gmake[4]: Leaving directory '/builds/worker/workspace/obj-build/security'
[task 2026-05-02T19:11:38.257+00:00] 19:11:38    ERROR -  ld64.lld: error: undefined symbol: _PR_Darwin_x86_64_AtomicIncrement
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  >>> referenced by pratom.c:245 (./../../../../../../checkouts/gecko/nsprpub/pr/src/misc/pratom.c:245)
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  >>>               ../config/external/nspr/pr/Unified_c_external_nspr_pr1.o:(symbol PR_AtomicIncrement+0x6)
[task 2026-05-02T19:11:38.257+00:00] 19:11:38    ERROR -  ld64.lld: error: undefined symbol: _PR_Darwin_x86_64_AtomicDecrement
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  >>> referenced by pratom.c:248 (./../../../../../../checkouts/gecko/nsprpub/pr/src/misc/pratom.c:248)
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  >>>               ../config/external/nspr/pr/Unified_c_external_nspr_pr1.o:(symbol PR_AtomicDecrement+0x6)
[task 2026-05-02T19:11:38.257+00:00] 19:11:38    ERROR -  ld64.lld: error: undefined symbol: _PR_Darwin_x86_64_AtomicSet
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  >>> referenced by pratom.c:252 (./../../../../../../checkouts/gecko/nsprpub/pr/src/misc/pratom.c:252)
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  >>>               ../config/external/nspr/pr/Unified_c_external_nspr_pr1.o:(symbol PR_AtomicSet+0x6)
[task 2026-05-02T19:11:38.257+00:00] 19:11:38    ERROR -  ld64.lld: error: undefined symbol: _PR_Darwin_x86_64_AtomicAdd
[task 2026-05-02T19:11:38.257+00:00] 19:11:38     INFO -  >>> referenced by pratom.c:256 (./../../../../../../checkouts/gecko/nsprpub/pr/src/misc/pratom.c:256)
[task 2026-05-02T19:11:38.258+00:00] 19:11:38     INFO -  >>>               ../config/external/nspr/pr/Unified_c_external_nspr_pr1.o:(symbol PR_AtomicAdd+0x6)
[task 2026-05-02T19:11:38.258+00:00] 19:11:38    ERROR -  clang: error: linker command failed with exit code 1 (use -v to see invocation)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.26%. Comparing base (6f7e664) to head (ca88731).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2692      +/-   ##
==========================================
- Coverage   74.27%   74.26%   -0.01%     
==========================================
  Files          70       70              
  Lines       39325    39333       +8     
==========================================
+ Hits        29208    29211       +3     
- Misses      10117    10122       +5     

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[AJIOB]

JFYI, looks like it's an implementation bug of the build system. Or we ignore something else, such as force switching language if it passed by command-line.

Pure GCC & clang calls doesn't preprocess pure .s files & it generates some another bugs, such as #2664, which is fixed by #2665.

We can precisely check in via e-mail or chatting if you want.

[sylvestre]

ok, thanks :)

what do you think we should do? :)

[AJIOB]

IMO, you should manually override the language for that files in your build system, such as pass the -x assembler-with-cpp from https://gcc.gnu.org/onlinedocs/gcc/Overall-Options.html to the compiler