posix: pthread: support for pthread_setcanceltype()

pthread_setcanceltype() is required by the POSIX_THREADS_BASE
Option Group as detailed in Section E.1 of IEEE-1003.1-2017.

The POSIX_THREADS_BASE Option Group is required for PSE51,
PSE52, PSE53, and PSE54 conformance, and is otherwise mandatory
for any POSIX conforming system as per Section A.2.1.3 of
IEEE-1003-1.2017.

Signed-off-by: Christopher Friedt <cfriedt@meta.com>