[Flang][OpenMP] Add source range for a few directives

[kiranchandramohan]

Summary

The sourcerange was missing for a few directives when
they were the first directive to appear in a program
without a program statement.

[kiranchandramohan]

Minor fix for taskwait test

[DavidTruby]

LGTM

flang/lib/Semantics/resolve-names.cpp

 
 // Create scopes for OpenMP constructs
 class OmpVisitor : public virtual DeclarationVisitor {
 public:
   void AddOmpSourceRange(const parser::CharBlock &);
 
   static bool NeedsScope(const parser::OpenMPBlockConstruct &);
 
+  bool Pre(const parser::OpenMPRequiresConstruct &x) {
+    AddOmpSourceRange(x.source);
+    return true;
+  }
+  bool Pre(const parser::OmpSimpleStandaloneDirective &x) {
+    AddOmpSourceRange(x.source);
+    return true;
+  }
   bool Pre(const parser::OpenMPBlockConstruct &);
   void Post(const parser::OpenMPBlockConstruct &);
   bool Pre(const parser::OmpBeginBlockDirective &x) {
     AddOmpSourceRange(x.source);
     return true;
   }
   void Post(const parser::OmpBeginBlockDirective &) {
     messageHandler().set_currStmtSource(std::nullopt);

flang/test/Semantics/OpenMP/barrier.f90

+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+
+!$omp barrier
+end

flang/test/Semantics/OpenMP/requires.f90

+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+
+!$omp requires reverse_offload
+end

flang/test/Semantics/OpenMP/taskwait.f90

+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+
+!$omp taskwait
+end