mingw32: merge checks for mingw-w64 and mingw32-runtime >= 3.15 into one

Originally committed as revision 24204 to svn://svn.ffmpeg.org/ffmpeg/trunk
(cherry picked from commit e26011d0f495de1148b8014995cbe923611b6b76)
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
1 file changed