By doing so, we essentially cover the various compiler flags that we
want to use for non-Visual Studio builds to check for warnings that
might cause real concern.
This also skips the checks for the various GCC-isque CFlag checks that
are scattered in the various build files on Visual Studio builds, since
they are essentially meaningless on Visual Studio builds.
This enables various compiler warnings project wide and disables the triggered
ones for each library/executable. This should give us roughly the same behaviour
as with autotools.
Tested with gcc8 and clang7.
glib_dep is what is actually needed to #include <glib.h>, not
gobject_dep. It works incidentally with system gobject/glib but not
when built via subprojects.
