gio: tests: rename generated giotypefunc.c to giotypefuncs.inc

This is needed for the Meson port, a file name .c that's included
and shouldn't be compiled into an object is difficult to manage
otherwise.

gio/tests/defaultvalue.c

@@ -174,7 +174,7 @@ list_all_types (void)
       GType *tp;
       all_registered_types = g_new0 (GType, 1000);
       tp = all_registered_types;
-#include "giotypefuncs.c"
+#include "giotypefuncs.inc"
       *tp = 0;
     }