[llvm] [MIRPrinter] Don't print line break when there is no instructions (NFC) (PR #80147)

[Quentin Dian via llvm-commits]

DianQK wrote:

Thanks for the review. I'll add `NFC` to the commit message, which should make it less painful for others to view the history.

https://github.com/llvm/llvm-project/pull/80147