nptl: Move legacy cancelation handling into libc as compat symbols

This affects _pthread_cleanup_pop, _pthread_cleanup_pop_restore,
_pthread_cleanup_push, _pthread_cleanup_push_defer.  The symbols
have been moved using scripts/move-symbol-to-libc.py.

No new symbol versions are added because the symbols are turned into
compatibility symbols at the same time.

__pthread_cleanup_pop and __pthread_cleanup_push are added as
GLIBC_PRIVATE symbols because they are also used internally, for
glibc's own cancellation handling.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>