win32, dos: Work around a bug in the GNU toolchain.

The bug[1] is exposed when gcc decides to put some data in a common
section (i.e. data that will be used by more than one object). It will
suggest the data to be aligned, but binutils >= 2.19 will fail to
properly align it. Thus if the data requires any alignment greater
than 4, the application will crash.
The workaround prevents gcc from putting data in a common section,
instead putting it in a properly aligned section.

[1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37216

Originally committed as revision 18501 to svn://svn.ffmpeg.org/ffmpeg/trunk