aarch64: Fix status return logic in RNG intrinsics

aarch64: Fix status return logic in RNG intrinsics

There is a bug with the RNG intrinsics in their return code. The definition says:

"Stores a 64-bit random number into the object pointed to by the argument and returns zero.
If the implementation could not generate a random number within a reasonable period of time
the object pointed to by the input is set to zero and a non-zero value is returned."

This means we should be testing whether to return non-zero with:
CSET W0, EQ
rather than NE.

This patch fixes that.

gcc/ChangeLog:

	* config/aarch64/aarch64-builtins.c (aarch64_expand_rng_builtin): Use EQ
	to compare against CC_REG rather than NE.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/acle/rng_2.c: New test.