* Makefile.in: Pass a new MULTILIB_EXCLUSIONS option as the sixth
	argument to genmultilib.
	* genmultilib: accept new MULTILIB_EXCLUSIONS option and output
	the contents into the multilib.h header.
	* gcc.c: Declare multilib_exclusions for the specs file.
	(set_multilib_dir): Use it.
	(print_multilib_info): Likewise.
	* t-linux64: Declare arguments for new MULTILIB_EXCLUSIONS option
	to pass to genmultilib.

From-SVN: r32365