nptl: Move pthread_getcpuclockid into libc

The symbol was moved using scripts/move-symbol-to-libc.py.

__libpthread_version_placeholder@@GLIBC_2.2 is needed by this change;
the Versions entry for GLIBC_2.2 in libpthread had leftover symbols
due to an error in a previous conflict resolution.  The condition
for the placeholder symbol is complicated because some architectures
have earlier symbols at the GLIBC_2.2 symbol versions, so the
placeholder is not required there (yet).

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