[clang][OpenMP] Shorten directive classification in ParseOpenMP (#94691)

Use directive categories to simplify long lists of `case` statements in
the OpenMP parser. This is a step towards avoiding dependence on
explicitly specified sets of directives that can be expressed more
generically.
The upcoming OpenMP 6.0 will introduce many new combined directives, and
the more generically we handle directives, the easier the introduction
of the new standard will be.

---------

Co-authored-by: Alexey Bataev <[email protected]>

Author: kparzysz

clang/include/clang/Parse/Parser.h

@@ -3511,6 +3511,19 @@ class Parser : public CodeCompletionHandler {
   /// metadirective and therefore ends on the closing paren.
   StmtResult ParseOpenMPDeclarativeOrExecutableDirective(
       ParsedStmtContext StmtCtx, bool ReadDirectiveWithinMetadirective = false);
+
+  /// Parses executable directive.
+  ///
+  /// \param StmtCtx The context in which we're parsing the directive.
+  /// \param DKind The kind of the executable directive.
+  /// \param Loc Source location of the beginning of the directive.
+  /// \param ReadDirectiveWithinMetadirective true if directive is within a
+  /// metadirective and therefore ends on the closing paren.
+  StmtResult
+  ParseOpenMPExecutableDirective(ParsedStmtContext StmtCtx,
+                                 OpenMPDirectiveKind DKind, SourceLocation Loc,
+                                 bool ReadDirectiveWithinMetadirective);
+
   /// Parses clause of kind \a CKind for directive of a kind \a Kind.
   ///
   /// \param DKind Kind of current directive.