MSVC builds: Update pre-defined cogl-define.h

...For both the regular WGL winsys and SDL winsys builds, that
COGL_HAS_GTYPE_SUPPORT is defined, so that the builds won't break as
Visual Studio builds do assume an existing installation of GLib.

Reviewed-by: Robert Bragg <robert@linux.intel.com>
cogl-texture-gl.c: Don't include strings.h unconditionally

Use the HAVE_STRINGS_H check before we include strings.h, as it is not
universally available.

Reviewed-by: Robert Bragg <robert@linux.intel.com>
cogl-gpu-info.c: Avoid using named initializers

Unfortunately named initializers is a feature that is not supported by
all compilers (such as pre-2013 Visual Studio) so avoid using that.

Reviewed-by: Robert Bragg <robert@linux.intel.com>