[llvm] [LLVM] Specialize LLVM lit test suites for `TableGen` and `FileCheck` with a smaller set of dependencies (PR #155929)

[Rahul Joshi via llvm-commits]

jurahul wrote:

> > but the lit tests run fine since all the dependencies specified do get rebuilt.
> 
> Or because the dependencies were found in the system.
> 
> I've once ran into this with `llc` missing from `clang/test/lit.cfg.py` (still not fixed). Spent an hour or so figuring out why the tests fail, and then another hour figuring out why llvm-lit uses llc installed in the system. (I must have done something obscure because llc is clearly in CLANG_TEST_DEPS, like deleting llc from disk or renaming the build directory before running the tests.)
> 
> These warnings should not be ignored and they can be confusing. Instead, we should specialize the list of needed tools per subdirectory (is it possible to add something to lit.local.cfg to achieve that?).
> 
> Not a blocker to me, but others may find the warnings confusing.

Right, so assuming the list of dependencies is correct, we get a warning for the *unused* dependencies and its benign. If the list of dependencies itself is missing, then you're right that this will end up using the command without substitution (from somewhere else or even from the same build/bin directory, just that it hasn't been rebuilt). This does not address that (or make it worse as well). Again, assuming the trimmed list of dependencies is kept correct

https://github.com/llvm/llvm-project/pull/155929