OpenMP 4.5 defines 'taskloop simd' directive, which is combined
directive for 'taskloop' and 'simd' directives. Patch adds initial
codegen support for this directive and its 2 basic clauses 'safelen' and
'simdlen'.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@267872 91177308-0d34-0410-b5e6-96231b3b80d8