ggml : suppress Windows compiler warnings (whisper/3075)

ggml : suppress Windows compiler warnings (whisper/3075)

* whisper: suppress Windows compiler warnings

This commit disables compiler warnings on window using MSVC.

The motivation for these changes is that some compilers generate
warnings for these conversion, for example Windows MSVC, and
there are quite a few of them. This makes it a little difficult to
spot new warnings that may be introduced and also can be difficult
for users/embedders of ggml where these warnings are hard to separate
from their own warnings.

* squash! whisper: suppress Windows compiler warnings

Move ggml related warnings into ggml. This commit also fixes the
indentation and adds a missing whitespace to the if statement.