src/common/win32: add missing casts

src/common/win32: add missing casts

clang errors out because of a few type mismatches that gcc
ignored through "-fpermissive".

We'll need to cast a few void pointers to the appropriate type.
There's also a function that doesn't have an explicit return type,
which was omitted by mistake.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>