LLVM backend: Emit i8 as place holder type for forward references again

(forward references aren't always resolved, so the backends need to handle
it still)

src/compiler/ir-llvm.bas

@@ -231,7 +231,7 @@ dim shared as const zstring ptr dtypeName(0 to FB_DATATYPES-1) = _
 	NULL        , _ '' struct
 	NULL        , _ '' namespace
 	NULL        , _ '' function
-	NULL        , _ '' fwd-ref
+	@"i8"       , _ '' fwd-ref
 	NULL          _ '' pointer
 }