[llvm] [DebugInfo] Don't apply is_stmt on MBB branches that preserve lines (PR #108251)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

> Hrm :/ what did you try testing?

Simple stage 2 build of clang, tried Debug and RelWithDebInfo with CMake defaults, with the commit applied and reverted. I didn't do split dwarf, but I don't think that should affect the line table size? If you have any more info on the config I might be able to try it out myself.

https://github.com/llvm/llvm-project/pull/108251