winpthreads: upgrade libtool

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6426 4407c894-4637-0410-b4f5-ada5f102cad1
winpthreads: upgrade libtool

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6427 4407c894-4637-0410-b4f5-ada5f102cad1