[flang] Silence bogus error on use after IMPORT

[klausler]

Summary

When a scope uses an explicit IMPORT statement to import a
symbol from the scope's host, it should not emit a bogus error
message later if that symbol is used in a specification construct.
The code that checks for imports being hidden by local declarations
was not allowing for the presence of host association (or USE)
indirection symbols in the local scope. Fix by using GetUltimate()
before checking for the hidden symbol.

[PeteSteinfeld]

Looks great! Thanks for doing this.

flang/lib/Semantics/resolve-names.cpp

case common::ImportKind::Only:
     }
     break;
   }
 }
 
 void ResolveNamesVisitor::CheckImport(
     const SourceName &location, const SourceName &name) {
   if (auto *symbol{FindInScope(name)}) {
+    const Symbol &ultimate{symbol->GetUltimate()};
+    if (&ultimate.owner() == &currScope()) {
       Say(location, "'%s' from host is not accessible"_err_en_US, name)
           .Attach(symbol->name(), "'%s' is hidden by this entity"_en_US,
               symbol->name());
     }
   }
+}
 
 bool ResolveNamesVisitor::Pre(const parser::ImplicitStmt &x) {
   return CheckNotInBlock("IMPLICIT") && // C1107
       ImplicitRulesVisitor::Pre(x);
 }
 
 void ResolveNamesVisitor::Post(const parser::PointerObject &x) {
   std::visit(common::visitors{

flang/test/Semantics/resolve29.f90

 ! RUN: %python %S/test_errors.py %s %flang_fc1
-module m
+module m1
   type t1
   end type
   type t3
   end type
   interface
     subroutine s1(x)
       !ERROR: 't1' from host is not accessible
       import :: t1
contains
   end
   subroutine s7()
     import, only: t1
     implicit none(external)
     !ERROR: 's5' is an external procedure without the EXTERNAL attribute in a scope with IMPLICIT NONE(EXTERNAL)
     call s5()
   end
 end module
+module m2
+  integer, parameter :: ck = kind('a')
+end module
+program main
+  use m2
+  interface
+    subroutine s0(x)
+      import :: ck
+      character(kind=ck) :: x ! no error
+    end subroutine
+  end interface
+end program