[flang] Prohibit MODULE procedures in the global scope

We were allowing procedures with the MODULE prefix to be declared at the global
scope.  This is prohibited by C1547 and was causing an internal check of the
compiler to fail.

I fixed this by adding a check.  I also added a test that would trigger a crash
without this change.

Differential Revision: https://reviews.llvm.org/D97875

Author: psteinfeld

flang/lib/Semantics/resolve-names.cpp

@@ -3157,6 +3157,13 @@ bool SubprogramVisitor::BeginMpSubprogram(const parser::Name &name) {
 // A subprogram declared with SUBROUTINE or FUNCTION
 bool SubprogramVisitor::BeginSubprogram(
     const parser::Name &name, Symbol::Flag subpFlag, bool hasModulePrefix) {
+  if (hasModulePrefix && currScope().IsGlobal()) { // C1547
+    Say(name,
+        "'%s' is a MODULE procedure which must be declared within a "
+        "MODULE or SUBMODULE"_err_en_US);
+    return false;
+  }
+
   if (hasModulePrefix && !inInterfaceBlock() &&
       !IsSeparateModuleProcedureInterface(
           FindSymbol(currScope().parent(), name))) {

flang/test/Semantics/resolve36.f90

@@ -2,6 +2,9 @@
 
 ! C1568 The procedure-name shall have been declared to be a separate module
 ! procedure in the containing program unit or an ancestor of that program unit.
+! C1547 MODULE shall appear only in the function-stmt or subroutine-stmt of a
+! module subprogram or of a nonabstract interface body that is declared in the
+! scoping unit of a module or submodule.
 module m1
   interface
     module subroutine sub1(arg1)
@@ -89,3 +92,8 @@ module subroutine b
   module procedure b
   end procedure
 end
+
+!ERROR: 'c1547' is a MODULE procedure which must be declared within a MODULE or SUBMODULE
+real module function c1547()
+  func = 0.0
+end function