Add parsing/sema analysis for 'simdlen' clause in simd directives. Also add check that if both 'safelen' and 'simdlen' clauses are specified, the value of 'simdlen' parameter is less than the value of 'safelen' parameter.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@245692 91177308-0d34-0410-b5e6-96231b3b80d8