[flang] 2.7.1 DO: Checks about clause arguments that allow Int Expr (flang-compiler/f18#540)

All the IntExpr argument checks are done through evaluating the result of GetIntValue. If the argument is non-constant integer expr, Expression Analysis will be the gatekeeper.


Original-commit: flang-compiler/f18@d8c4804828c1f9f68088940a50c1380a18a72987
Reviewed-on: https://github.com/flang-compiler/f18/pull/540