backport: re PR target/91481 (POWER9 "DARN" RNG intrinsic produces repeated output...

backport: re PR target/91481 (POWER9 "DARN" RNG intrinsic produces repeated output (CVE-2019-15847))

	Backport from trunk
	2019-08-22  Segher Boessenkool  <segher@kernel.crashing.org>

	PR target/91481
	* config/rs6000/rs6000.md (unspec): Delete UNSPEC_DARN, UNSPEC_DARN_32,
	and UNSPEC_DARN_RAW.
	(unspecv): New enumerator values UNSPECV_DARN, UNSPECV_DARN_32, and
	UNSPECV_DARN_RAW.
	(darn_32): Use an unspec_volatile, and UNSPECV_DARN_32.
	(darn_raw): Use an unspec_volatile, and UNSPECV_DARN_RAW.
	(darn): Use an unspec_volatile, and UNSPECV_DARN.

From-SVN: r275185