[llvm] lit: improve long path support on Windows (PR #207250)

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``````````bash
darker --check --diff -r origin/main...HEAD llvm/utils/lit/lit/InprocBuiltins.py llvm/utils/lit/lit/ShellEnvironment.py
``````````

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``````````diff
--- InprocBuiltins.py	2026-07-02 18:44:03.000000 +0000
+++ InprocBuiltins.py	2026-07-02 18:49:59.990129 +0000
@@ -178,11 +178,11 @@
 
     def extended(path):
         if not kIsWindows:
             return path
         path = os.path.abspath(path)
-        if path.startswith('\\\\'):
+        if path.startswith("\\\\"):
             return "\\\\?\\UNC\\{0}".format(path[2:])
         return "\\\\?\\{0}".format(path)
 
     stderr = StringIO()
     exitCode = 0
--- ShellEnvironment.py	2026-07-02 18:44:03.000000 +0000
+++ ShellEnvironment.py	2026-07-02 18:50:00.058544 +0000
@@ -120,11 +120,11 @@
 
     def extended(path):
         if not kIsWindows:
             return path
         path = os.path.abspath(path)
-        if path.startswith('\\\\'):
+        if path.startswith("\\\\"):
             return "\\\\?\\UNC\\{0}".format(path[2:])
         return "\\\\?\\{0}".format(path)
 
     # Apply the redirections, we use (N,) as a sentinel to indicate stdin,
     # stdout, stderr for N equal to 0, 1, or 2 respectively. Redirects to or

``````````

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https://github.com/llvm/llvm-project/pull/207250