Update test and place it into Lower.

Author: valerydmit

flang/test/Lower/generic-shadows-specific.F90

@@ -0,0 +1,40 @@
+
+#if STEP == 1
+! these modules must be read from  module files
+module generic_shadows_specific_m1
+  interface f ! reference must be to generic
+    module procedure f ! must have same name as generic interface
+  end interface
+ contains
+  character function f() ! must be character
+    f = 'q'
+  end
+end
+module generic_shadows_specific_m2
+   use generic_shadows_specific_m1
+end
+module generic_shadows_specific_m3
+   use generic_shadows_specific_m2 ! must be generic_shadows_specific_m2, not generic_shadows_specific_m1
+ contains
+   subroutine mustExist() ! not called, but must exist
+     character x
+     x = f()
+   end
+end
+
+#else
+! Check that expected code produced with no crash.
+subroutine reproducer()
+  use generic_shadows_specific_m2
+  use generic_shadows_specific_m3
+  character x
+  x = f()
+end
+#endif
+
+!RUN: rm -rf %t && mkdir -p %t
+!RUN: %flang_fc1 -fsyntax-only -DSTEP=1 -J%t %s
+!RUN: %flang_fc1 -emit-fir -J%t -o - %s | FileCheck %s
+
+!CHECK-LABEL: func.func @_QPreproducer
+!CHECK: fir.call @_QMgeneric_shadows_specific_m1Pf