cris: Enable "neg" to set condition codes.

cris: Enable "neg" to set condition codes.

While gcc seems to prefer transforming tests on the result of
reversible operations, into tests on the original, it also can
work with the destination, if allocated to the same register as
it commonly-enough is.  The re-use is easily covered in a
test-case.  (N.B.: the value 0x80000000 appears to be considered
invalid and unimportant.)  Spotted as a "microregression" in
libgcc when comparing to the cc0 version.

gcc:
	* config/cris/cris.c (cris_select_cc_mode): Return CC_NZmode for
	NEG too.  Correct comment.
	* config/cris/cris.md ("<anz>neg<mode>2<setnz>"): Rename from
	"neg<mode>2".