Allow parentheses around the _Cilk_for and simd for condition

- this is consistent with the loop increment.
Only ignore parentheses not other casts
Cilk plus elemental functions - parsing through to metadata.

Template support TBD.
Cilk Plus elemental functions.

Parsing through to metadata generation.
Template support TBD.
Fix spurious attribute warnings.

Incorrectly checking for duplicate attribute names caused some to
disappear.
Correct tests corresponding to warning message case consistency fix.
Fix a bug in Cilk for adjustment expression

- A rvalue is required as the right hand side of the adjustment
  binary expression.

- The reproducer added.
Emit an error when simd clause is delimited by anything other than a space
- Always emit an error when a non-identifier is encountered in #pragma simd
- Also fixes cases like:
  #pragma simd;
  #pragma simd , vectorlength(4)