Since htl does not actually need a stack switch, we can initialize it
like nptl is, avoiding all sorts of startup issues with ifunc.
More precisely, htl defines __pthread_initialize_minimal instead of the
elder _cthread_init_routine. We can then drop the stack switching dances.
libpthread_syms.a will contain the symbols that libc tries to get from
libpthread, to be used by the system, but also by tests.
* htl/libpthread.a, htl/libpthread_pic.a: Link libpthread_syms.a and Move EXTERN
references to...
* htl/libpthread_syms.a: ... new file. Add missing
__pthread_enable_asynccancel reference.
* htl/Makefile: Install libpthread_syms.a and link it into static tests.
