clang: target: Include gcc-m-fpu.cmake file

File gcc-m-fpu.cmake is responsible for determining what should be
passed to -mfpu option. Fortunately GCC and Clang options are compatible
so we can use the file for clang.

The list of supported -mfpu options can be found at
https://github.com/llvm/llvm-project

 in
llvm/include/llvm/TargetParser/ARMTargetParser.def file.

Signed-off-by: Patryk Duda <pdk@semihalf.com>