cc-wrapper-test: add tests for `--`

  name = "cc-wrapper-test";

  buildCommand = ''

    set -o pipefail

    NIX_DEBUG=1 $CC -v

    NIX_DEBUG=1 $CXX -v

      ''}

    ''}

    ${# See: https://github.com/llvm/llvm-project/commit/ed1d07282cc9d8e4c25d585e03e5c8a1b6f63a74

      # `gcc` does not support this so we gate the test on `clang`

      lib.optionalString stdenv.cc.isClang ''

        printf "checking whether cc-wrapper accepts -- followed by positional (file) args..." >&2

        mkdir -p positional

        # Make sure `--` is not parsed as a "non flag arg"; we should get an

        # input file error here and *not* a linker error.

        { ! $CC --; } |& grep -q "no input files"

        # And that positional file args _must_ be files (this is just testing

        # that we remembered to put the `--` back in the args to the compiler):

        { ! $CC -c -- -o foo ${./foo.c}; } \

          |& grep -q "no such file or directory: '-o'"

        # Now check that we accept single and multiple positional file args:

        $CC -c -DVALUE=42 -o positional/foo.o -- ${./foo.c}

        $CC -o positional/main -- positional/foo.o ${./ldflags-main.c}

        ${emulator} ./positional/main

    ''}

    printf "checking whether compiler uses NIX_CFLAGS_COMPILE... " >&2

    mkdir -p foo/include

    cp ${./foo.c} foo/include/foo.h