Partially reverting 5b1c6d30

* mms-bitfields causes a decrease in speed by ~30%
* Although it's use is recommended for compatibility reasons, it's seemingly not necessary for us anyway (so far)

build.sh

@@ -741,8 +741,6 @@ build_mac()
 build_win32()
 {
     export CPPFLAGS="-D_WIN32_WINDOWS=0x0410 $CPPFLAGS"
-    export CFLAGS="-mms-bitfields $CFLAGS"
-    export CXXFLAGS="-mms-bitfields $CXXFLAGS"
 
     prepare_mingw || failure
     build_mingw || failure