Enable gcc option -mms-bitfield for Mingw32 and cygwin gcc.

Enable gcc option -mms-bitfield for Mingw32 and cygwin gcc.
(Only configure.in is edited.)
Modified Files:
   Makefile.in aclocal.m4 configure configure.in
   autoconf/Makefile.in configs/Makefile.in doc/Makefile.in
   doc/C/Makefile.in doc/ja_JP.eucJP/Makefile.in
   interface/Makefile.in interface/bitmaps/Makefile.in
   interface/motif_bitmaps/Makefile.in
   interface/pixmaps/Makefile.in libarc/Makefile.in
   libunimod/Makefile.in script/Makefile.in timidity/Makefile.in
   utils/Makefile.in
: