stop using libgthread internally

The gobject tools (glib-genmarshal and gobject-query) were linking
against libgthread.  Stop that.

Also, remove the gthread_INCLUDES internal automake substitution.

configure.ac

@@ -3564,14 +3564,9 @@ AC_SUBST(config_h_INCLUDES)
 glib_INCLUDES='$(config_h_INCLUDES) -I$(top_builddir)/glib -I$(top_srcdir)/glib -I$(top_srcdir)'
 AC_SUBST(glib_INCLUDES)
 
-# gthread:
-#   same as glib
-gthread_INCLUDES='$(glib_INCLUDES)'
-AC_SUBST(gthread_INCLUDES)
-
 # gobject:
-#   same as gthread
-gobject_INCLUDES='$(gthread_INCLUDES)'
+#   same as glib
+gobject_INCLUDES='$(glib_INCLUDES)'
 AC_SUBST(gobject_INCLUDES)
 
 # gmodule:

gobject/Makefile.am

@@ -14,7 +14,7 @@ CLEANFILES=
 
 AM_CPPFLAGS = 					\
 	-DG_LOG_DOMAIN=\"GLib-GObject\"		\
-	$(gthread_INCLUDES) 			\
+	$(glib_INCLUDES)			\
 	$(GLIB_DEBUG_FLAGS)			\
 	-DGOBJECT_COMPILATION
 
@@ -27,7 +27,7 @@ TESTS = abicheck.sh
 endif
 endif
 
-libglib = $(top_builddir)/glib/libglib-2.0.la $(top_builddir)/gthread/libgthread-2.0.la
+libglib = $(top_builddir)/glib/libglib-2.0.la
 
 # libraries to compile and install
 lib_LTLIBRARIES = libgobject-2.0.la