[flang] Accept compiler directives between module subprograms (#91230)

Parse and represent compiler directives in a modules
module-subprogram-part between the module subprograms.

Author: klausler

flang/include/flang/Parser/parse-tree.h

@@ -2905,7 +2905,8 @@ struct ModuleSubprogram {
   UNION_CLASS_BOILERPLATE(ModuleSubprogram);
   std::variant<common::Indirection<FunctionSubprogram>,
       common::Indirection<SubroutineSubprogram>,
-      common::Indirection<SeparateModuleSubprogram>>
+      common::Indirection<SeparateModuleSubprogram>,
+      common::Indirection<CompilerDirective>>
       u;
 };
 

flang/lib/Parser/program-parsers.cpp

@@ -247,7 +247,8 @@ TYPE_CONTEXT_PARSER("module subprogram part"_en_US,
 //         separate-module-subprogram
 TYPE_PARSER(construct<ModuleSubprogram>(indirect(functionSubprogram)) ||
     construct<ModuleSubprogram>(indirect(subroutineSubprogram)) ||
-    construct<ModuleSubprogram>(indirect(Parser<SeparateModuleSubprogram>{})))
+    construct<ModuleSubprogram>(indirect(Parser<SeparateModuleSubprogram>{})) ||
+    construct<ModuleSubprogram>(indirect(compilerDirective)))
 
 // R1410 module-nature -> INTRINSIC | NON_INTRINSIC
 constexpr auto moduleNature{