[llvm] [LIT][Cygwin] Mark `ulimit -n` unsupported for Cygwin (PR #164604)

[Tomohiro Kashiwada via llvm-commits]

https://github.com/kikairoya created https://github.com/llvm/llvm-project/pull/164604

Cygwin doesn't support `ulimit -n` because Windows doesn't provide such functionality.

>From 4407b0b7979ba3eaecf9f6b16e3d79d9aa31f8ae Mon Sep 17 00:00:00 2001
From: kikairoya <kikairoya at gmail.com>
Date: Wed, 22 Oct 2025 20:14:33 +0900
Subject: [PATCH] [LIT][Cygwin] Mark `ulimit -n` unsupported for Cygwin

Cygwin doesn't support `ulimit -n` because Windows doesn't provide such functionality.
---
 llvm/utils/lit/lit/run.py             | 4 ++--
 llvm/utils/lit/tests/shtest-ulimit.py | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/llvm/utils/lit/lit/run.py b/llvm/utils/lit/lit/run.py
index 62070e824e87f..5830b21be6b0f 100644
--- a/llvm/utils/lit/lit/run.py
+++ b/llvm/utils/lit/lit/run.py
@@ -137,6 +137,6 @@ def _increase_process_limit(self):
                     "Raised process limit from %d to %d" % (soft_limit, desired_limit)
                 )
         except Exception as ex:
-            # Warn, unless this is Windows or z/OS, in which case this is expected.
-            if os.name != "nt" and platform.system() != "OS/390":
+            # Warn, unless this is Windows, z/OS, or Cygwin in which case this is expected.
+            if os.name != "nt" and platform.system() != "OS/390" and platform.sys.platform != "cygwin":
                 self.lit_config.warning("Failed to raise process limit: %s" % ex)
diff --git a/llvm/utils/lit/tests/shtest-ulimit.py b/llvm/utils/lit/tests/shtest-ulimit.py
index 9a8febd3333c4..c3d51067e8936 100644
--- a/llvm/utils/lit/tests/shtest-ulimit.py
+++ b/llvm/utils/lit/tests/shtest-ulimit.py
@@ -3,7 +3,7 @@
 # ulimit does not work on non-POSIX platforms.
 # Solaris for some reason does not respect ulimit -n, so mark it unsupported
 # as well.
-# UNSUPPORTED: system-windows, system-solaris
+# UNSUPPORTED: system-windows, system-cygwin, system-solaris
 
 # RUN: not %{lit} -a -v %{inputs}/shtest-ulimit --order=lexical | FileCheck %s