libpthread glibc nptl testsuite

For fun and profit we should run glibc's NPTL testsuite against libpthread.

Also, there are sometimes issues fixed in NPTL that libpthread should also be checked against. Totally incomplete list:

pthread_cancel when single-threaded, glibc 439bf404b8fa125cf950dc1aa37838702c5353ea, sourceware [BZ #13613], id:"20120509202437.268a72b9@spoyarek".
__libc_stack_end, glibc 9c6ea9facbba4d430807bd21fa82892d713b1ecd, 18b5e737de22462ab6b3fc89f26c9ad480ebb843, sourceware [BZ #12416], id:"20120419120021.4780e8c8@spoyarek", id:"20120615005913.4f517e02@spoyarek", id:"[email protected]".