This patch adds the semantic check for occurrence of constructs nested inside a SIMD region.
To make the test generalized for multiple constructs, to avoid repeats, the check is done while Enter()-ing the top level OpenMPConstruct
Also adds a test case.
It also modifies an existing test case for nested ordered clause check because with the current check introduced, the previous test shows two sema check failures instead of one.
PS: The check is currently supporting SIMD loops, but not declare SIMD directive.