AArch64: Fix overflow in memcopy expansion on aarch64.

AArch64: Fix overflow in memcopy expansion on aarch64.

Currently the inline memcpy expansion code for AArch64 is using a signed int
to hold the number of elements to copy.  When you giver give it a value larger
than INT_MAX it will overflow.

The overflow causes the maximum number of instructions we want to expand to
check to fail since this assumes an unsigned number.

This patch changes the maximum isns arithmetic to be unsigned HOST_WIDE_INT.

note that the calculation *must* remained signed as the memcopy issues
overlapping unaligned copies.  This means the pointer must be moved back and
so you need signed arithmetic.

gcc/ChangeLog:

	PR target/97535
	* config/aarch64/aarch64.c (aarch64_expand_cpymem): Use unsigned
	arithmetic in check.

gcc/testsuite/ChangeLog:

	PR target/97535
	* gcc.target/aarch64/pr97535.c: New test.