[CMake] Move -Wno-unused-but-set-parameter from MLIR up to LLVM (#221824)
This warning is known to have false positives with GCC versions before
14.
Since 3aec6a40bb4e49f9ea181ac5c949b6c7c20a5465, this warning appears
when building LLVMSupport as well - thus move the disabling of the
warning up from MLIR to all of LLVM.
In HandleLLVMOptions, the common procedure is to not check for whether
the options are supported or not, but to just hardcode the version
ranges where the options are supported, per compiler.
This option (and -Wunused-but-set-parameter) is available in GCC since
long before our minimum required version.