automakify building the static libpthread.a library as essentially just a copy of the static winpthreads library.  The _DEPS line is required so that dependencies, and thus parallel builds, work

git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5787 4407c894-4637-0410-b4f5-ada5f102cad1
automakify the shared version of libpthread.a (or rather, the dll import lib)

git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5788 4407c894-4637-0410-b4f5-ada5f102cad1