[llvm] [AArch64][BTI] Mark EH landing pads as jump targets (PR #149680)

[Benjamin Herrenschmidt via llvm-commits]

ozbenh wrote:

So bear with me, I have no idea what I'm doing, never looked at LLVM code that deep, and this is probably completely wrong ... but hacking `AArch64BranchTargets::addBTI()` this way:

```
-  BuildMI(MBB, MBB.begin(), MBB.findDebugLoc(MBB.begin()),
-          TII->get(AArch64::HINT))
+  for (MBBI = MBB.begin() ; MBBI != MBB.end() && MBB.isEHPad(); MBBI++)
+         if (MBBI->getOpcode() == TargetOpcode::EH_LABEL) {
+                 MBBI++;
+                 break;
+         }
+  BuildMI(MBB, MBBI, MBB.findDebugLoc(MBBI), TII->get(AArch64::HINT))
       .addImm(HintNum);
 ```

Seems to do the trick :-)

I don't know how the `HasWinCFI` bit right before is affected if at all, again I have no idea what I'm doing, I mostly just grepped `EH_LABEL` and tried to make uniformed deductions :-)

https://github.com/llvm/llvm-project/pull/149680