whisper : enable compiler warnings for src (#2891)

whisper : enable compiler warnings for src (#2891)

* whisper : enable compiler warnings for src

This commit enables compiler warnings for the src directory. Currently
when the WHISPER_ALL_WARNINGS flag is set to ON is only enables warnings
in ggml, by setting GGML_ALL_WARNINGS to ON. This commit adds the same
compiler flags for whisper's src directory.

The motivation for this is to catch potential bugs and issues early on
in the development process.

* squash! whisper : enable compiler warnings for src

Remove GF_C_FLAGS and GF_CXX_FLAGS from add_compile_options.