Building both shared and static libraries is now possible on MinGW.

patch by Zuxy Meng, zuxy.meng gmail com

Originally committed as revision 9030 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1161,15 +1161,6 @@ case $targetos in
   mingw32*)
     targetos=mingw32
     shlibdir="$bindir"
-    if enabled_all shared static; then
-        cat <<EOF
-You can only build one library type at once on MinGW.
-Specify --disable-static --enable-shared to only build
-the shared libraries. To build only the static libraries
-you do not need to pass additional options.
-EOF
-        exit 1
-    fi
     dv1394="no"
     ffserver="no"
     network="no"