[AArch64] Add support for SVE absolute comparisons

[AArch64] Add support for SVE absolute comparisons

This patch adds support for floating-point absolute comparisons
FACLT and FACLE (aliased as FACGT and FACGE with swapped operands).

2019-08-14  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/iterators.md (SVE_COND_FP_ABS_CMP): New iterator.
	* config/aarch64/aarch64-sve.md (*aarch64_pred_fac<cmp_op><mode>):
	New pattern.

gcc/testsuite/
	* gcc.target/aarch64/sve/vcond_21.c: New test.
	* gcc.target/aarch64/sve/vcond_21_run.c: Likewise.

From-SVN: r274443