[llvm] [X86] Fix RegAlloc issue by implementing TRI::getCustomEHPadPreservedMask (PR #135518)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

The first commit contains a test. I can craft a mir test instead if necessary, but it is going to be much less readable.


https://github.com/llvm/llvm-project/pull/135518