--- gcc-6.4.0-orig/gcc/c-family/cppspec.c	2017-07-24 16:03:41.665352594 +0100
+++ gcc-6.4.0/gcc/c-family/cppspec.c	2017-07-24 16:23:05.633928359 +0100
@@ -197,3 +197,9 @@
 
 /* Number of extra output files that lang_specific_pre_link may generate.  */
 int lang_specific_extra_outfiles = 0;  /* Not used for cpp.  */
+
+/* lang_register_spec_functions.  Not used for cpp.  */
+void
+lang_register_spec_functions (void)
+{
+}
