cstore patterns always have a scalar integer result, which has the
value 0 for "false" and STORE_FLAG_VALUE for "true".  This patch
makes that explicit using scalar_int_mode.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* target.def (cstore_mode): Return a scalar_int_mode.
	* doc/tm.texi: Regenerate.
	* config/sparc/sparc.c (sparc_cstore_mode): Return a scalar_int_mode.
	* targhooks.h (default_cstore_mode): Likewise.
	* targhooks.c (default_cstore_mode): Likewise, using a forced
	conversion.
	* expmed.c (emit_cstore): Expect the target of the cstore to be
	a scalar_int_mode.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r251489