Split out parts of scompare_loc_descriptor and emit_store_flag

This patch splits some cases out of scompare_loc_descriptor and
emit_store_flag, which helps with the upcoming machmode series.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* dwarf2out.c (scompare_loc_descriptor_wide)
	(scompare_loc_descriptor_narrow): New functions, split out from...
	(scompare_loc_descriptor): ...here.
	* expmed.c (emit_store_flag_int): New function, split out from...
	(emit_store_flag): ...here.

From-SVN: r251451