Fix omp_sections_nowait.c test to address Bugzilla Bug 28336

This rewrite of the omp_sections_nowait.c test file causes it to hang if the
nowait is not respected. If the nowait isn't respected, the lone thread which
can escape the first sections construct will just sleep at a barrier which
shouldn't exist. All reliance on timers is taken out. For good measure, the test
makes sure that all eight sections are executed as well. The test should take no
longer than a few seconds on any modern machine.

Differential Revision: http://reviews.llvm.org/D21842

llvm-svn: 274151