[llvm] [llvm] Allow Fast and Tail CC in UEFI (PR #138361)

[Prabhu Rajasekaran via llvm-commits]

Prabhuk wrote:

> test coverage?

Thank you. Added tests. One of the tests will fail until  https://github.com/llvm/llvm-project/pull/138602 lands.

https://github.com/llvm/llvm-project/pull/138361