[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]

================
@@ -746,11 +746,25 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
                     env_str = "\n".join(
                         f"{key}={value}" for key, value in sorted(cmd_shenv.env.items())
                     )
-                    results.append(
-                        ShellCommandResult(
-                            j, env_str, "", 0, timeoutHelper.timeoutReached(), []
-                        )
+                    # Process redirections.
+                    stdin, stdout, stderr = processRedirects(
+                        j, default_stdin, cmd_shenv, opened_files
                     )
+                    if stdout != default_stdin:
----------------
arichardson wrote:

Is this always true? I admit I didn't try to understand all of processRedirects, but it doesn't look like the input argument is ever returned for `stdout`?

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