[clang] [StrTable] Mechanically convert Hexagon builtins to use TableGen (PR #123460)

[Chandler Carruth via cfe-commits]

chandlerc wrote:

> Thanks @chandlerc this is great! I think I'd seen multiple reviews where someone saw the preprocessor tricks and suggested it was more suitable for tablegen. Too bad we hadn't done it before now, but many thanks to you for doing it.
> 
> I was able to do some fairly minimal regression testing with this change (I rebuilt the linux toolchain and ran a small subset of `llvm-test-suite` in `qemu-hexagon`), all passed. Unfortunately there's no architecture-specific builtins among those tests, so it's not a whole lot of confidence gained there.
> 
> @iajbar can you please review this change (or perhaps it would be more useful to review the conversion script)? I think your review would make more sense than mine. Note that I did try the `Q6_V_vgetqfextor_VVR` test case that you recently enabled - that still compiles successfully after this change.

FWIW, I don't think extensive testing is terribly necessary here.

I verified that after this change the `.inc` file generated by TableGen has exactly equivalent `TARGET_BUILTIN` X-macros, but in a different order. Here is the Fish shell code I used to diff things:

```fish
diff -u (rg -I '^TARGET' BuiltinsHexagon{,Dep}.def | sd ' +' ' ' | sd ',"' ', "' | sort | psub)  (rg '^TARGET' dev/tools/clang/include/clang/Basic/BuiltinsHexagon.inc | sd -f c '"v([0-9]+)\|[^"]+"' 'V$1' | sd '"hvxv([0-9][0-9])\|[^"]+"' 'HVXV$1' | sd '"hvxv79"' 'HVXV79' | sort |psub)
```

This should sort the builtins, fix different whitespace, and map the expanded feature string literals used in TableGen to the macro names used in the `.def` files. It uses a few less common tools like `rg`, RipGrep, and `sd`, https://github.com/chmln/sd.

> Also, Chandler - can you update the commit message to describe which sha was used as the input to `hexagon_builtinify.py`? This is nice for posterity IMO.

I used the exact version deleted in this PR, from the parent commit of this PR's commit, https://github.com/llvm/llvm-project/commit/7253c6fde498c4c9470b681df47d46e6930d6a02 -- I will add that to the PR description as well.

I also so comments on the python script, but as I mentioned there, the script is not code I'm suggesting to check in or maintain, merely documenting for completeness. It was never written to be remotely readable or clean, just to produce a verifiably equivalent TableGen file.

https://github.com/llvm/llvm-project/pull/123460