[llvm] [lit] Add stream-injectable run() core to builtin cat (PR #204711)

[Prasoon Kumar via llvm-commits]

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@@ -26,7 +27,14 @@ def convertToCaretAndMNotation(data):
     return newdata.getvalue().encode()
 
 
-def main(argv):
+def run(argv, stdin, stdout, stderr, cwd):
+    """In-process cat
+
+    stdin / stdout / stderr are binary streams and cwd is the
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prasoon054 wrote:

Done!

https://github.com/llvm/llvm-project/pull/204711