[libc][aarch64] Use inline_memcpy_aligned_access_64bit under -mstrict-align (#227428)

Under `-mstrict-align`, clang cannot determine both `src` and `dst` are
aligned. The end of `inline_memcpy_aarch64` aligns `src` but it cannot
confirm `dst` is aligned. As a result,
`builtin::Memcpy<64>::loop_and_tail(dst, src, count)` lowers to
`__builtin_memcpy_inline(..., 64)` but clang emits many many single-byte
load/store instructions to ensure correctness. This can be very slow, so
if unaligned accesses are not supported, opt for adjusting both `src`
and `dst` such that we can use 8-byte loads/stores.
`inline_memcpy_aligned_access_64bit` already does this so we can just
reuse that.

GitOrigin-RevId: f35bd33e2d9037a2dab48c8231355e01b9c4a722