[OMPT] Create infrastructure and add first tests for OMPT

Some basic checks next to the implementation should futher lower the
possibility to introduce regressions. (Note that this would have catched
the ordering issue fixed in rL258866 and pointed to rL263940.)

The tests are implementation dependent in one point because they assume that
thread ids are assigned in ascending order. This is not defined by the standard
but currently ensured in libomp. We have to think about another way of ordering
the threads should this ever be subject to change...

Note that this isn't aiming at replacing the implementation independent
test-suite at https://github.com/OpenMPToolsInterface/ompt-test-suite!

Differential Revision: http://reviews.llvm.org/D16715

llvm-svn: 264027