[libcxx-commits] [libcxx] [libc++] Remove explicit mentions of __need_FOO macros (PR #119025)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Now I get:

```
CMake Error at /usr/share/cmake-3.28/Modules/CMakeTestCCompiler.cmake:67 (message):
  The C compiler

    "/usr/bin/clang-19"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: '/tmp/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-byXI6P'

    Run Build Command(s): /usr/bin/ninja -v cmTC_b2c1b
    [1/2] /usr/bin/clang-19 --sysroot=/tmp/sysroot-linux    -MD -MT CMakeFiles/cmTC_b2c1b.dir/testCCompiler.c.o -MF CMakeFiles/cmTC_b2c1b.dir/testCCompiler.c.o.d -o CMakeFiles/cmTC_b2c1b.dir/testCCompiler.c.o -c /tmp/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-byXI6P/testCCompiler.c
    [2/2] : && /usr/bin/clang-19 --sysroot=/tmp/sysroot-linux  --rtlib=compiler-rt --unwindlib=libunwind CMakeFiles/cmTC_b2c1b.dir/testCCompiler.c.o -o cmTC_b2c1b   && :
    FAILED: cmTC_b2c1b
    : && /usr/bin/clang-19 --sysroot=/tmp/sysroot-linux  --rtlib=compiler-rt --unwindlib=libunwind CMakeFiles/cmTC_b2c1b.dir/testCCompiler.c.o -o cmTC_b2c1b   && :
    /usr/bin/ld: cannot find -lunwind: No such file or directory
    clang-19: error: linker command failed with exit code 1 (use -v to see invocation)
    ninja: build stopped: subcommand failed.
  ```
  
Sorry, but I can't play whack-a-mole like that. Can you please provide a working reproducer (e.g. a script that sets up the necessary Docker image + CMake invocation), a pre-commit CI bot that catches it, or perform the analysis of why this is now failing yourself? Otherwise, that isn't really workable -- this patch is correct according to our CI, and that's how we determine what's supported. I don't want to be pedantic and use that criterion to dismiss arbitrary breakage, but we do need to draw a line about where contributor responsibility ends and consumers' responsibility begins, otherwise folks can offload arbitrary troubleshooting to us.

https://github.com/llvm/llvm-project/pull/119025