[llvm] [AArch64][GlobalISel] Fail legalization for unknown libcalls. (PR #81873)

[Kiran Chandramohan via llvm-commits]

https://github.com/kiranchandramohan approved this pull request.

Thanks @davemgreen for the fix. Could we have this in the release branch too? We have an internal team that requires this for their tests to pass.

https://github.com/llvm/llvm-project/pull/81873