A "BTI c" instruction only allows jumping/calling to using a BLR* instruction.
However, the SLSBLR mitigation changes a BLR to a BR to implement the
function call. Therefore, a "BTI c" check that passed before could
trigger after the BLR->BL change done by the SLSBLR mitigation.
However, if the register used in BR is X16 or X17, this trigger will not
fire (see ArmARM for further details).
Therefore, this patch simply changes the function stubs for the SLSBLR
br x<N> SpeculationBarrier
mov x16, x<N> br x16 SpeculationBarrier