Don't use the internal _G_DEFINE_TYPE_EXTENDED_CLASS_INIT macro

This macro is internal to gobject so using it risks breaking Cogl if
glib changes its API. Instead we just use its expansion. Note that
glib provides two expansions for this depending on the glib version
but this only uses the one for older versions.

Reviewed-by: Robert Bragg <robert.bragg@intel.com>
mingw: Try adding a -w64 suffix when searching for a suitable compiler

On 64-bit fedora the 32-bit MinGW compiler is called
i686-w64-mingw32-gcc which wasn't being picked up by the
mingw-fetch-depdencies script.

Reviewed-by: Robert Bragg <robert.bragg@intel.com>
(cherry picked from commit f5f0342315e524523c50549e91eb9ff1683ab558)