[flang] Fix bug with IMPORT of USE of USE

When a module contained an import of a use-association of a
use-association, we weren't recognizing that the symbols was needed.
The fix is the follow all of the use-associations using `GetUltimate()`.

Differential Revision: https://reviews.llvm.org/D79737

Author: tskeith

flang/lib/Semantics/mod-file.cpp

@@ -833,7 +833,7 @@ void SubprogramSymbolCollector::Collect() {
   for (const auto &pair : scope_) {
     const Symbol &symbol{*pair.second};
     if (const auto *useDetails{symbol.detailsIf<UseDetails>()}) {
-      if (useSet_.count(useDetails->symbol()) > 0) {
+      if (useSet_.count(useDetails->symbol().GetUltimate()) > 0) {
         need_.push_back(symbol);
       }
     }

flang/test/Semantics/modfile36.f90

@@ -0,0 +1,41 @@
+! RUN: %S/test_modfile.sh %s %t %f18
+
+! Check modfile that contains import of use-assocation of another use-association.
+
+module m1
+  interface
+     subroutine s(x)
+       use, intrinsic :: iso_c_binding, only: c_ptr
+       type(c_ptr) :: x
+     end subroutine
+  end interface
+end module
+!Expect: m1.mod
+!module m1
+! interface
+!  subroutine s(x)
+!   use iso_c_binding, only: c_ptr
+!   type(c_ptr) :: x
+!  end
+! end interface
+!end
+
+module m2
+  use, intrinsic :: iso_c_binding, only: c_ptr
+  interface
+     subroutine s(x)
+       import :: c_ptr
+       type(c_ptr) :: x
+     end subroutine
+  end interface
+end module
+!Expect: m2.mod
+!module m2
+! use iso_c_binding,only:c_ptr
+! interface
+!  subroutine s(x)
+!   import::c_ptr
+!   type(c_ptr)::x
+!  end
+! end interface
+!end