[llvm] [CI] Disable flang from pre-commit tests when Flang files are not touched (PR #93485)

[Kiran Chandramohan via llvm-commits]

kiranchandramohan wrote:

> > This is a bit of a weird take to me: what does "officially in production" mean? Did MLIR ever got "officially in production" in the context of the LLVM project? The only thing I'm aware of is the notion of "experimental", which applies to backends (Flang was kind of in-between at the beginning because it was C++17 before LLVM was, but it's all aligned now). There are degrees of maturity of course, but I haven't seen issues with the Flang-on-Linux CI so far (some frontend files are annoyingly heavy to compile!), or only very occasionally (flaky tests can happen, but not more than in LLVM itself or any other project)
> 
> Our main support policy is: https://llvm.org/docs/SupportPolicy.html I have reported at least three serious issues with Flang testing since last year, all of which took over a month to get fixed. This one is only the last example.

This issue did take some time to fix because it was not reproducible on any of the Windows machines we tried. One of the past issues that was brought up (https://github.com/llvm/llvm-project/issues/77086) was a bot issue as pointed out by @joker-eph in https://github.com/llvm/llvm-project/issues/77086#issuecomment-1878905702. I don't remember what the third issue was.

https://github.com/llvm/llvm-project/pull/93485