Fix missing assemble_external in ASM_OUTPUT_FDESC

When TARGET_VTABLE_USES_DESCRIPTORS is defined then function pointers in
the vtable are output by ASM_OUTPUT_FDESC.  The only current user of
this is ia64, but its implementation of ASM_OUTPUT_FDESC lacks a call to
assemble_external.  Thus if there is no other reference to the function
the weak declaration for it will be missing.

	PR target/95154
	* config/ia64/ia64.h (ASM_OUTPUT_FDESC): Call assemble_external.

gcc/config/ia64/ia64.h

@@ -963,6 +963,7 @@ do {									\
 do {									\
   if ((PART) == 0)							\
     {									\
+      assemble_external (DECL);						\
       if (TARGET_ILP32)							\
         fputs ("\tdata8.ua @iplt(", FILE);				\
       else								\