aarch64 SFrame: use preferred CFI directive for AArch64 PAC

ARMv8.3 addded support for a new security feature named Pointer
Authentication. Support for this feature in SFrame already exists.

In GCC 14 and older, the Sparc DWARF extension .cfi_gnu_window_save
is emitted instead of .cfi_negate_ra_state.
GCC 15 fixed this issue, but this behavior is preserved for backward
compatibility.

The existing sframe test for AArch64 PAC was using .cfi_gnu_window_save.
This patch replaces this CFI in the existing test by the preferred one,
and adds a new test to check for backward compatibility when using
.cfi_gnu_window_save.

Approved-by: Indu Bhagat <indu.bhagat@oracle.com>