[cmake] Silence a duplicate libraries warning from Apple's linker (#85012)

ld: warning: ignoring duplicate libraries:

This triggers quite frequently in llvm's build because CMake's library
depends mechanism doesn't de-duplicate libraries on the link line.
Duplication is necessary for ELF platforms, but means something subtly
different on Darwin platforms, hence the warning. Since we don't have
much control over that from CMake, just disable the warning wholesale
whenever the linker is detected to support it.