* Makefile.in (s-mlib): Don't build multilibs if
	--disable-multilib.
	(DRIVER_DEFINES): Adjust accordingly.
	(gcc.o): Likewise.
	(protoize.o): Likewise.
	(unprotoize.o): Likewise.
	* configure.in: Recognize --enable-multilib.

	* Makefile.in (g++spec.o): Adjust use of DRIVER_DEFINES.

From-SVN: r39452