c++: Over-zealous assert [PR 99239]

[Nathan Sidwell]

This was simply	an overzealous assert.	Possibly correct thinking at the 
time that code was written, but not true now.  Of course we can have 
imported artificial decls.

        PR c++/99239
        gcc/cp/
        * decl.c (duplicate_decls): Remove assert about maybe-imported
        artificial decls.
        gcc/testsuite/
        * g++.dg/modules/pr99239_a.H: New.
        * g++.dg/modules/pr99239_b.H: New.

--
Nathan Sidwell
diff --git c/gcc/cp/decl.c w/gcc/cp/decl.c
index 8e8f37d060e..289db3074be 100644
--- c/gcc/cp/decl.c
+++ w/gcc/cp/decl.c
@@ -2041,8 +2041,6 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
     {
       if (DECL_ARTIFICIAL (olddecl))
 	{
-	  gcc_checking_assert (!(DECL_LANG_SPECIFIC (olddecl)
-				 && DECL_MODULE_IMPORT_P (olddecl)));
 	  if (!(global_purview_p () || not_module_p ()))
 	    error ("declaration %qD conflicts with builtin", newdecl);
 	  else
diff --git c/gcc/testsuite/g++.dg/modules/pr99239_a.H w/gcc/testsuite/g++.dg/modules/pr99239_a.H
new file mode 100644
index 00000000000..35f006fe9b2
--- /dev/null
+++ w/gcc/testsuite/g++.dg/modules/pr99239_a.H
@@ -0,0 +1,13 @@
+// PR 99239 ICE on catch clause
+// { dg-additional-options -fmodule-header }
+// { dg-module-cmi {} }
+
+inline void Foo ()
+{
+  try
+    {}
+  catch(...)
+    {
+    }
+}
+
diff --git c/gcc/testsuite/g++.dg/modules/pr99239_b.H w/gcc/testsuite/g++.dg/modules/pr99239_b.H
new file mode 100644
index 00000000000..92638d663c7
--- /dev/null
+++ w/gcc/testsuite/g++.dg/modules/pr99239_b.H
@@ -0,0 +1,12 @@
+// { dg-additional-options {-fmodule-header -fno-module-lazy} }
+// { dg-module-cmi {} }
+import  "pr99239_a.H";
+       
+inline void
+  _M_remove_reference() throw()
+{
+  try
+    { }
+  catch(...)
+    { }
+}