aarch64: add PAC GNU property note to libgcc lse.S

aarch64: add PAC GNU property note to libgcc lse.S

This note is not used anywhere currently but it is supposed to mark
objects if the return address is protected with PAC on the stack.
Since lse.S only has leaf functions the return address is never
saved on the stack so we can add the note.

The note is only added if pac-ret is enabled because it can cause
problems with old linkers and we don't have checks for that. This
can be changed later to be unconditional, for now it is consistent
with how gcc generates the notes.

libgcc/ChangeLog:

	* config/aarch64/lse.S: Add PAC property note.