fixes for building in mingw

diff -r orig/vgmstream-master/Makefile vgmstream-master/Makefile
0a1,3
>
> #export MINGW_PREFIX=i586-mingw32msvc-
>
diff -r orig/vgmstream-master/ext_libs/Makefile.mingw vgmstream-master/ext_libs/Makefile.mingw
2c2
< export DLLTOOL=i586-mingw32msvc-dlltool
---
> export DLLTOOL=$(MINGW_PREFIX)dlltool
11a12,14
>
> libat3plusdecoder.a: at3plusdecoder.def
>   $(DLLTOOL) -d at3plusdecoder.def -l libat3plusdecoder.a
14c17
<   rm -f libvorbis.a libmpg123-0.a libg7221_decode.a
---
>   rm -f libvorbis.a libmpg123-0.a libg7221_decode.a libat3plusdecoder.a
diff -r orig/vgmstream-master/src/Makefile vgmstream-master/src/Makefile
24c24,25
<     coding/mtaf_decoder.o
---
>     coding/mtaf_decoder.o\
>     coding/at3_decoder.o
295c296,297
<     meta/bcstm.o
---
>     meta/bcstm.o \
>     meta/fsb5.o
diff -r orig/vgmstream-master/src/coding/coding.h vgmstream-master/src/coding/coding.h
73a74
> #if defined(VGM_USE_MP4V2) && defined(VGM_USE_FDKAAC)
74a76
> #endif
diff -r orig/vgmstream-master/test/Makefile.mingw vgmstream-master/test/Makefile.mingw
2,6c2,7
< export CFLAGS=-Wall -O3 -DVGM_USE_G7221 -I../ext_includes
< export LDFLAGS=-L../src -L../ext_libs -lvgmstream -lvorbis -lmpg123-0 -lg7221_decode -lm
< export CC=i586-mingw32msvc-gcc
< export AR=i586-mingw32msvc-ar
< export STRIP=i586-mingw32msvc-strip
---
> export CFLAGS=-Wall -O3 "-DVGM_USE_G7221" "-DVGM_USE_MAIATRAC3PLUS" -I../ext_includes
> export LDFLAGS=-L../src -L../ext_libs -static-libgcc -lvgmstream -lvorbis -lmpg123-0 -lg7221_decode -lat3plusdecoder
> export CC=$(MINGW_PREFIX)gcc
> export AR=$(MINGW_PREFIX)ar
> export STRIP=$(MINGW_PREFIX)strip
> export WINDRES=$(MINGW_PREFIX)windres
23a25,27
>   $(MAKE) -C ../ext_libs -f Makefile.mingw $@
>
> libat3plusdecoder.a:
diff -r orig/vgmstream-master/version.sh vgmstream-master/version.sh
3c3
< VERSION="`svnversion "$DIR" | tr : _`"
---
> VERSION=BLAH
diff -r orig/vgmstream-master/winamp/Makefile vgmstream-master/winamp/Makefile
2,7c2,7
< export CFLAGS=-Wall -O3 "-DVGM_USE_G7221" -I../ext_includes
< export LDFLAGS=-L../src -L../ext_libs -lvgmstream -lvorbis -lmpg123-0 -lg7221_decode -lm
< export CC=i586-mingw32msvc-gcc
< export AR=i586-mingw32msvc-ar
< export STRIP=i586-mingw32msvc-strip
< export WINDRES=i586-mingw32msvc-windres
---
> export CFLAGS=-Wall -O3 "-DVGM_USE_G7221" "-DVGM_USE_MAIATRAC3PLUS" -I../ext_includes
> export LDFLAGS=-L../src -L../ext_libs -static-libgcc -lvgmstream -lvorbis -lmpg123-0 -lg7221_decode -lat3plusdecoder
> export CC=$(MINGW_PREFIX)gcc
> export AR=$(MINGW_PREFIX)ar
> export STRIP=$(MINGW_PREFIX)strip
> export WINDRES=$(MINGW_PREFIX)windres
9c9
< .PHONY: libvgmstream.a libvorbis.a libmpg123-0.a libg7221_decode.a
---
> .PHONY: libvgmstream.a libvorbis.a libmpg123-0.a libg7221_decode.a libat3plusdecoder.a
11c11
< in_vgmstream.dll: libvgmstream.a libvorbis.a libmpg123-0.a libg7221_decode.a in_vgmstream.c resource.o
---
> in_vgmstream.dll: libvgmstream.a libvorbis.a libmpg123-0.a libg7221_decode.a libat3plusdecoder.a in_vgmstream.c resource.o
27a28,30
>   $(MAKE) -C ../ext_libs -f Makefile.mingw $@
>
> libat3plusdecoder.a:
diff -r orig/vgmstream-master/winamp/in_vgmstream.c vgmstream-master/winamp/in_vgmstream.c
101a102
>   "at3\0AT3 Audio File (*.AT3)\0",