[llvm] [llvm-lit] Add redirection handling for `env` command without args and write a lit test to check behavior with lit internal shell (PR #106629)

[Alexander Richardson via llvm-commits]

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@@ -0,0 +1,7 @@
+## Test the env command with output redirection to a file.
+# RUN: rm -f %t
+# RUN: env > %t
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arichardson wrote:

I can see from the code that the redirect is only consumed if there are no arguments, but could we also check that `env VAR=value > %t` and `env A=B echo "no env output here please"` behave as expected?

https://github.com/llvm/llvm-project/pull/106629