allow 'extern "C" ' coroutines.

gistfile1.txt

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 3f23317a315..c1a0d6c2283 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -32,6 +32,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree.h"
 #include "gcc-rich-location.h"
 #include "hash-map.h"
+#include "cgraph.h"
 
 static bool coro_promise_type_found_p (tree, location_t);
 
@@ -4060,6 +4061,17 @@ coro_build_actor_or_destroy_function (tree orig, tree fn_type,
       else
        info->destroy_decl = fn;
     }
+  /* If the function is extern "C" the mangler will not be called.  */
+  if (DECL_EXTERN_C_P (orig))
+    {
+      /* clone_function_name () picks up the name from DECL_ASSEMBLER_NAME
+        which is not yet set here.  */
+      SET_DECL_ASSEMBLER_NAME (fn, DECL_NAME (orig));
+      if (actor_p)
+       SET_DECL_ASSEMBLER_NAME (fn, clone_function_name (fn, "actor"));
+      else
+       SET_DECL_ASSEMBLER_NAME (fn, clone_function_name (fn, "destroy"));
+    }
   return fn;
 }
 

just because one can do something ... does not mean one should (I'm still not exactly sure about when this would be useful and whether it was intended in the design - question to core to follow).