[aarch64/64821]: Simplify __builtin_aarch64_sqrt* into internal function .SQRT.

[aarch64/64821]: Simplify __builtin_aarch64_sqrt* into internal function .SQRT.

This is a simple patch which simplifies the __builtin_aarch64_sqrt* builtins
into the internal function SQRT which allows for constant folding and other
optimizations at the gimple level. It was originally suggested we do to
__builtin_sqrt just for __builtin_aarch64_sqrtdf when -fno-math-errno
but since r6-4969-g686ee9719a4 we have the internal function SQRT which does
the same so it makes we don't need to check -fno-math-errno either now.

Applied as approved after bootstrapped and tested on aarch64-linux-gnu with no regressions.

	PR target/64821

gcc/ChangeLog:

	* config/aarch64/aarch64-builtins.cc
	(aarch64_general_gimple_fold_builtin): Handle
	__builtin_aarch64_sqrt* and simplify into SQRT internal
	function.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/vsqrt-1.c: New test.
	* gcc.target/aarch64/vsqrt-2.c: New test.