[llvm] [lit] add `LIT_MAX_WORKERS` env variable (PR #76205)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-testing-tools

Author: Maksim Levental (makslevental)

<details>
<summary>Changes</summary>

I find myself fiddling with `ARGS "-j"` very frequently when switching between groups of tests with `LIT_FILTER`. Then invariably I accidentally commit `ARGS "-j1"` or something like that. This env variable (analogous to `LIT_FILTER`) resolves the issue. 

Not sure how to test but I'm pretty sure this is "correct code".

---
Full diff: https://github.com/llvm/llvm-project/pull/76205.diff


1 Files Affected:

- (modified) llvm/utils/lit/lit/cl_arguments.py (+1-1) 


``````````diff
diff --git a/llvm/utils/lit/lit/cl_arguments.py b/llvm/utils/lit/lit/cl_arguments.py
index ba3706659550b6..b9122d07afd8a1 100644
--- a/llvm/utils/lit/lit/cl_arguments.py
+++ b/llvm/utils/lit/lit/cl_arguments.py
@@ -36,7 +36,7 @@ def parse_args():
         metavar="N",
         help="Number of workers used for testing",
         type=_positive_int,
-        default=lit.util.usable_core_count(),
+        default=os.getenv("LIT_MAX_WORKERS", lit.util.usable_core_count()),
     )
     parser.add_argument(
         "--config-prefix",

``````````

</details>


https://github.com/llvm/llvm-project/pull/76205