[llvm] [MIR] Allow overriding isSSA, noPhis, noVRegs in MIR input (PR #108546)

[Vladimir Vereschaka via llvm-commits]

vvereschaka wrote:

> LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-expensive-checks-debian` running on `gribozavr4` while building `llvm` at step 6 "test-build-unified-tree-check-all".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/16/builds/5941
> 
> Here is the relevant piece of the build log for the reference

also https://lab.llvm.org/buildbot/#/builders/187/builds/1416

https://github.com/llvm/llvm-project/pull/108546