[OpenMP] add check for both simdlen and safelen clauses specified

This patch adds the check for specifying both simdlen and safelen clauses on the 'distribute simd' or 'distribute parallel for simd' constructs.

Differential Revision: https://reviews.llvm.org/D22384


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@275529 91177308-0d34-0410-b5e6-96231b3b80d8