[llvm] [lit] Implement builtin umask (PR #94621)

[Jay Foad via llvm-commits]

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@@ -4,7 +4,6 @@
 ## Windows has no umask so this test makes no sense, nor would
 ## it work because there is no umask(1) in a Windows environment
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jayfoad wrote:

Seems fine to me. I didn't write the original comment. Perhaps it was trying to explain that Windows has neither umask(1) nor umask(2) ?!

https://github.com/llvm/llvm-project/pull/94621