[BUG] Tests fail to build with clang-20

[jdoubleu]

Describe the bug
I noticed, that the unit tests fail to build with clang-20:

c++: error: argument unused during compilation: '-c' [-Werror,-Wunused-command-line-argument]
gmake[2]: *** [test/CMakeFiles/state_assembly_test.dir/build.make:76: test/CMakeFiles/state_assembly_test.dir/state_assembly_test.cc.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:1771: test/CMakeFiles/state_assembly_test.dir/all] Error 2
gmake[1]: *** Waiting for unfinished jobs....
c++: error: argument unused during compilation: '-c' [-Werror,-Wunused-command-line-argument]
c++: error: argument unused during compilation: '-c' [-Werror,-Wunused-command-line-argument]
gmake[2]: *** [test/CMakeFiles/donotoptimize_assembly_test.dir/build.make:76: test/CMakeFiles/donotoptimize_assembly_test.dir/donotoptimize_assembly_test.cc.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:1719: test/CMakeFiles/donotoptimize_assembly_test.dir/all] Error 2
gmake[2]: *** [test/CMakeFiles/clobber_memory_assembly_test.dir/build.make:76: test/CMakeFiles/clobber_memory_assembly_test.dir/clobber_memory_assembly_test.cc.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:1823: test/CMakeFiles/clobber_memory_assembly_test.dir/all] Error 2

System
Which OS, compiler, and compiler version are you using:

• OS: Linux 5.15.167.4
• Compiler and version: clang 20.1.2

To reproduce
Steps to reproduce the behavior:

docker run --rm -it silkeh/clang:20 sh -c '
apt update && apt install -y git cmake;
mkdir /app && cd /app;
git clone https://github.com/google/benchmark.git;
cmake -B build -S benchmark/ -DBENCHMARK_DOWNLOAD_DEPENDENCIES=ON;
cmake --build build/ --parallel;'

Additional context
I find the error messages odd; this might be a CMake issue.

Using cmake --build build/ --verbose I get the following output for the compile command:

[ 62%] Building CXX object test/CMakeFiles/state_assembly_test.dir/state_assembly_test.cc.o
cd /app/build/test && /usr/bin/c++ -DBENCHMARK_STATIC_DEFINE -DHAVE_POSIX_REGEX -DHAVE_PTHREAD_AFFINITY -DHAVE_STD_REGEX -DHAVE_STEADY_CLOCK -DHAVE_THREAD_SAFETY_ATTRIBUTES -DTEST_BENCHMARK_LIBRARY_HAS_NO_ASSERTIONS -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE -I/app/benchmark/include -Wall  -Wextra  -Wshadow  -Wfloat-equal  -Wold-style-cast  -Wconversion  -Werror  -pedantic  -pedantic-errors  -Wshorten-64-to-32  -fstrict-aliasing  -Wno-deprecated-declarations  -Wno-deprecated  -Wstrict-aliasing  -Wthread-safety  -Wno-unused-variable -fvisibility=hidden -fvisibility-inlines-hidden   -UNDEBUG -S -O3 -g0 -fno-stack-protector -std=c++17 -MD -MT test/CMakeFiles/state_assembly_test.dir/state_assembly_test.cc.o -MF CMakeFiles/state_assembly_test.dir/state_assembly_test.cc.o.d -o CMakeFiles/state_assembly_test.dir/state_assembly_test.cc.o -c /app/benchmark/test/state_assembly_test.cc
gmake[2]: Leaving directory '/app/build'
/usr/bin/gmake  -f test/CMakeFiles/repetitions_test.dir/build.make test/CMakeFiles/repetitions_test.dir/build
gmake[2]: Entering directory '/app/build'
gmake[2]: Leaving directory '/app/build'
/usr/bin/gmake  -f test/CMakeFiles/cxx11_test.dir/build.make test/CMakeFiles/cxx11_test.dir/build
c++: error: argument unused during compilation: '-c' [-Werror,-Wunused-command-line-argument]
gmake[2]: *** [test/CMakeFiles/clobber_memory_assembly_test.dir/build.make:76: test/CMakeFiles/clobber_memory_assembly_test.dir/clobber_memory_assembly_test.cc.o] Error 1
gmake[2]: Leaving directory '/app/build'
gmake[1]: *** [CMakeFiles/Makefile2:1823: test/CMakeFiles/clobber_memory_assembly_test.dir/all] Error 2
gmake[2]: Entering directory '/app/build'
c++: error: argument unused during compilation: '-c' [-Werror,-Wunused-command-line-argument]

[jdoubleu]

This might also be a clang issue, after all: llvm/llvm-project#100909 (comment)