[llvm-lit] Print environment variables when using env without subcommand (#98414)

This patch addresses an issue with lit's internal shell when env is
without any arguments, it fails with exit code 127 because `env`
requires a subcommand. This patch addresses the issue by encoding the
command to properly return environment variables even when no arguments
are provided.

The error occurred when running the command 
` LIT_USE_INTERNAL_SHELL=1 ninja check-llvm`.

fixes: #102383
This is part of the test cleanups proposed in the RFC: [[RFC] Enabling
the Lit Internal Shell by
Default](https://discourse.llvm.org/t/rfc-enabling-the-lit-internal-shell-by-default/80179)

Author: Harini0924

llvm/utils/lit/lit/TestRunner.py

@@ -742,7 +742,16 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
                     cmd_shenv = ShellEnvironment(shenv.cwd, shenv.env)
                 args = updateEnv(cmd_shenv, args)
                 if not args:
-                    raise InternalShellError(j, "Error: 'env' requires a" " subcommand")
+                    # Return the environment variables if no argument is provided.
+                    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(), []
+                        )
+                    )
+                    return 0
             elif args[0] == "not":
                 not_args.append(args.pop(0))
                 not_count += 1

llvm/utils/lit/tests/Inputs/shtest-env/env-calls-cd.txt renamed to llvm/utils/lit/tests/Inputs/shtest-env-negative/env-calls-cd.txt

@@ -7,4 +7,5 @@ config.test_source_root = None
 config.test_exec_root = None
 config.environment["FOO"] = "1"
 config.environment["BAR"] = "2"
+config.environment["QUX"] = "3"
 config.substitutions.append(("%{python}", '"%s"' % (sys.executable)))