The file /usr/include/glib.h, at line 66, includes the file glibconfig.h; It is missing. The glib.h file is from rpm glib-devel-1.2.6-3 of 6.2 for intel. (All 6.2 packages have been installed.) This makes the gtk development impossible.
Found the glibconfig.h file in /usr/lib/glib/include/glibconfig.h. Don't understand why this is in a separate directory; no other files in that directory.
Sorry, my fault. I didn't know about glib-config and ctk-config when I had the problem.