[flang] A separate module procedure must inherit interface attributes

[klausler]

Summary

Attributes like PURE, ELEMENTAL, &c. are specified on the interface of
a separate module procedure, so when the MODULE PROCEDURE is defined in
a submodule, it must acquire those attributes from the interface.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Semantics/resolve-names.cpp

for (const Symbol *dummyArg : details.dummyArgs()) {
       } else if (Symbol * copy{currScope().CopySymbol(*dummyArg)}) {
         newDetails.add_dummyArg(*copy);
       }
     }
     if (details.isFunction()) {
       currScope().erase(symbol->name());
       newDetails.set_result(*currScope().CopySymbol(details.result()));
     }
+    newSymbol.attrs() |= symbol->attrs();
   }
   return true;
 }
 
 // A subprogram or interface declared with SUBROUTINE or FUNCTION
 bool SubprogramVisitor::BeginSubprogram(const parser::Name &name,
     Symbol::Flag subpFlag, bool hasModulePrefix,
     const parser::LanguageBindingSpec *bindingSpec,

flang/test/Semantics/separate-mp02.f90

 submodule(m7) sm7
 contains
   !ERROR: Dummy argument 1 of 's1' is an alternate return indicator but the corresponding argument in the interface body is not
   !ERROR: Dummy argument 2 of 's1' is not an alternate return indicator but the corresponding argument in the interface body is
   module subroutine s1(*, x)
     real :: x
   end
 end
+
+module m8
+  interface
+    pure elemental module subroutine s1
+    end subroutine
+  end interface
+end module
+submodule(m8) sm8
+ contains
+  !Ensure no spurious error about mismatching attributes
+  module procedure s1
+  end procedure
+end submodule