[AArch64] Implement TARGET_GIMPLE_FOLD_BUILTIN for aarch64 backend.

[AArch64] Implement TARGET_GIMPLE_FOLD_BUILTIN for aarch64 backend.

gcc/
	* config/aarch64/aarch64-builtins.c
	(aarch64_gimple_fold_builtin): New.
	* config/aarch64/aarch64-protos.h (aarch64_gimple_fold_builtin): New.
	* config/aarch64/aarch64-simd-builtins.def (addv): New.
	* config/aarch64/aarch64-simd.md (addpv4sf): New.
	(addvv4sf): Update.
	* config/aarch64/aarch64.c (TARGET_GIMPLE_FOLD_BUILTIN): Define.

gcc/testsuite/
	* gcc.target/aarch64/vaddv-intrinsic.c: New.
	* gcc.target/aarch64/vaddv-intrinsic-compile.c: Likewise.
	* gcc.target/aarch64/vaddv-intrinsic.x: Likewise.

Co-Authored-By: Tejas Belagod <tejas.belagod@arm.com>
From-SVN: r198304