[clang] [llvm] Reland "[Utils] Add new --update-tests flag to llvm-lit" (PR #153821)

[Henrik G. Olsson via llvm-commits]

hnrklssn wrote:

> > It also adds support for auto-fixing tests failing based on the diff command.
> 
> This seems like an independent feature -- do it as a followup?

Will do

https://github.com/llvm/llvm-project/pull/153821