In #5492, I did not build the benchmarks because I didn't know how to get google-benchmark built for ARM64EC. Now I seem to find the solution.

To create static libraries for ARM64EC, the /machine:arm64ec option needs to be passed to lib.exe. CMake doc mentions that the STATIC_LIBRARY_OPTIONS target property holds the options for lib.exe. This means benchmarks/CMakeLists.txt needs to set this property for each relevant target, including those defined by google-benchmark. But it turns out that CMAKE_STATIC_LINKER_FLAGS will also be passed to lib.exe.

Setting CMAKE_STATIC_LINKER_FLAGS is simpler, and it affects every target, including those added in the future (either by us or by google-benchmark), which is desirable in this specific case. So this PR chooses to set CMAKE_STATIC_LINKER_FLAGS.

(Note: it seems that CMAKE_STATIC_LINKER_FLAGS defaults to /machine:arm64, so I decided to override it instead of appending /machine:arm64ec to it, but appending might be more future-proof.)

(Note 2: just in case you are interested: stl/CMakeLists.txt handles this by adding ${VCLIBS_EXPLICIT_MACHINE} to the STATIC_LIBRARY_OPTIONS target property for every relevant target, where ${VCLIBS_EXPLICIT_MACHINE} is /machine:arm64ec for ARM64EC and empty otherwise.)