[OpenMP] Detect implicit map type to report unspecified map type for target...

[OpenMP] Detect implicit map type to report unspecified map type for target enter/exit data directives.

Support for the following OpenMP 4.5 restriction on 'target enter data' and 'target exit data':

  - A map-type must be specified in all map clauses.

I have to save 'IsMapTypeImplicit' when parsing a map clause to support this constraint and for more informative error messages. This helps me support the following case:

  #pragma omp target enter data map(r) // expected-error {{map type must be specified for '#pragma omp target enter data'}}

and distinguish it from:

  #pragma omp target enter data map(tofrom: r) // expected-error {{map type 'tofrom' is not allowed for '#pragma omp target enter data'}}

Patch by Arpith Jacob. Thanks!

llvm-svn: 258179