d: Fix multiple definition error when using mixins and interfaces.

gcc/d/ChangeLog:

	PR d/92216
	* decl.cc (make_thunk): Don't set TREE_PUBLIC on thunks if the target
	function is external to the current compilation.

gcc/testsuite/ChangeLog:

	PR d/92216
	* gdc.dg/imports/pr92216.d: New.
	* gdc.dg/pr92216.d: New test.

gcc/d/ChangeLog

+2020-03-16  Iain Buclaw  <ibuclaw@gdcproject.org>
+
+	PR d/92216
+	* decl.cc (make_thunk): Don't set TREE_PUBLIC on thunks if the target
+	function is external to the current compilation.
+
 2020-01-01  Jakub Jelinek  <jakub@redhat.com>
 
 	Update copyright years.

gcc/d/decl.cc

@@ -1803,8 +1803,11 @@ make_thunk (FuncDeclaration *decl, int offset)
 
   DECL_CONTEXT (thunk) = d_decl_context (decl);
 
-  /* Thunks inherit the public access of the function they are targetting.  */
-  TREE_PUBLIC (thunk) = TREE_PUBLIC (function);
+  /* Thunks inherit the public access of the function they are targetting.
+     When the function is outside the current compilation unit however, then the
+     thunk must be kept private to not conflict.  */
+  TREE_PUBLIC (thunk) = TREE_PUBLIC (function) && !DECL_EXTERNAL (function);
+
   DECL_EXTERNAL (thunk) = 0;
 
   /* Thunks are always addressable.  */

gcc/testsuite/ChangeLog

+2020-03-16  Iain Buclaw  <ibuclaw@gdcproject.org>
+
+	PR d/92216
+	* gdc.dg/imports/pr92216.d: New.
+	* gdc.dg/pr92216.d: New test.
+
 2020-03-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/94179

gcc/testsuite/gdc.dg/imports/pr92216.d

+module imports.pr92216;
+
+class B : I
+{
+    protected override void getStruct(){}
+    mixin A!();
+
+}
+
+mixin template A()
+{
+    public void* getS()
+    {
+        return null;
+    }
+}
+
+public interface I
+{
+    public void* getS();
+    protected void getStruct();
+}

gcc/testsuite/gdc.dg/pr92216.d

+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92216
+// { dg-options "-I $srcdir/gdc.dg" }
+// { dg-do compile }
+// { dg-final { scan-assembler "_DT16_D7imports7pr922161B8__mixin24getSMFZPv\[: \t\n\]" } }
+// { dg-final { scan-assembler-not "(.globl|.global)\[ 	\]+_DT16_D7imports7pr922161B8__mixin24getSMFZPv" } }
+module pr92216;
+
+private import imports.pr92216;
+
+class C : B
+{
+    protected override void getStruct() {}
+}