[libc++][test] Use `ADDITIONAL_COMPILE_FLAGS(gcc-style-warnings)` for `-Wno-psabi` (#113608)
MSVC doesn't understand `-Wno-psabi`, which was introduced here by
@ldionne in #106077.
Using `ADDITIONAL_COMPILE_FLAGS(gcc-style-warnings)` (implemented by
#75317) avoids passing this to MSVC.