[ARC] Deprecate mexpand-adddi option.

[ARC] Deprecate mexpand-adddi option.

Emitting subregs in the expand will result in broken code due to LRA handling of them. Issue observed while turning on mlra and mexpand-adddi options using dejagnu test suite. Deprecate this
option.

gcc/
2017-04-26  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.md (adddi3): Remove support for mexpand-adddi
	option.
	(subdi3): Likewise.
	* config/arc/arc.opt (mexpand-adddi): Deprecate it.
	* doc/invoke.texi (mexpand-adddi): Update text.

From-SVN: r250276