thread_pthread.c: fallback to CLOCK_REALTIME
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63244 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
thread_pthread.c: fallback to CLOCK_REALTIME
CLOCK_REALTIME when failed to set to CLOCK_MONOTONIC, e.g. on
Solaris. [Misc #14497]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63244 b2dd03c8-39d4-4d8f-98ff-823fe69b080e