linux(4): Fix clock_nanosleep return value for unsupported clockid.

The Linux clock_nanosleep() returns ENOTSUP for CLOCK_THREAD_CPUTIME_ID.
This silence one of the LTP clock_nanosleep tests.

MFC after: 2 weeks

(cherry picked from commit 66e73ce7371b717b8dd0dfd6e3deeacfa95e6f8b)