[llvm][AArch64] Fix an interaction of SLS and BTI after a returns twice call

This fixes the combination of two things:
* Placing a BTI after calls to a returns twice function like setjmp.
  This allows the setjmp to return with a br instead of a ret.
* Straight line speculation mitigations that replace BLR with a BL
  to a thunk that does the mitigation, and then goes to the original
  target.

Originally I marked AArch64call_bti as requiring that SLS mitigation
be disabled. This caused a crash when you tried to codegen with both.
Since CALL_BTI tried to match with AArch64call_bti but could not.

This change does 2 things:
* Follow the pattern set by AArch64call and add 2 patterns for
  AArch64call_bti. One with no IP (interprocedural) registers,
  and one with. For SLS mitigation on and off respectively.
* Modify the sls hardening pass to iterate through bundled
  instructions, as the AArch64 KCFI pass does.

Since there is a 1:1 replacement of the BLR with a BL,
the bundle remains intact. This is checked with an MIR test.

The ir -> asm testing is updated to add runs with the sls
mitigation enabled.

Reviewed By: kristof.beyls, pzheng

Differential Revision: https://reviews.llvm.org/D143915

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