Make OpenMP autoconf test actually test inclusion of <omp.h>
Make OpenMP autoconf test actually test inclusion of <omp.h>

We expect to be able to #include <omp.h> in libmesh, so this test
should reflect that.

Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh