Cleanup the sources for libmingwex.  In the process, I found that _rotr64.c and _rotl64.c were listed under both 32-only and 64-only, so I moved them to the common area after checking with Ozkan.

git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@5255 4407c894-4637-0410-b4f5-ada5f102cad1