mutex.c: Don't return EBUSY if mutex' busy-state is set.  Instead wait for zero-state.
cond.c:  Make sure busy is set to zero and remove useless check.
barrier.c: Fix wrong trylock by blocking lock


git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@6471 4407c894-4637-0410-b4f5-ada5f102cad1