cmake: Add some more utility functions.

For C/C++ preprocessor additions:
- add_c_preproc_definition
- add_cxx_preproc_definition
- add_preproc_definition

For required flags:
- require_c_flag(_/nomsvc)
- require_cxx_flag(_/nomsvc)
- require_flag(_/nomsvc)

Change-Id: If72a8901e39ddb95305415e33ec3368cdd28a754
2 files changed