configure: properly check for mingw-w64 through installed headers. mingw-w64 can also target 32-bit code.

Originally committed as revision 24156 to svn://svn.ffmpeg.org/ffmpeg/trunk
(cherry picked from commit 0a4307d6307516d333ce2cde2a2ffa0f50bc176c)
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
1 file changed