Move the change to test/Shell subdirctory & update to not set

environment variable.

Author: cmtice

lldb/test/Shell/lit.cfg.py

@@ -21,7 +21,15 @@
 config.name = "lldb-shell"
 
 # testFormat: The test format to use to interpret tests.
-config.test_format = toolchain.ShTestLldb(not llvm_config.use_lit_shell)
+# We prefer the lit internal shell which provides a better user experience on
+# failures and is faster unless the user explicitly disables it with
+# LIT_USE_INTERNAL_SHELL=0 env var.
+use_lit_shell = True
+lit_shell_env = os.environ.get("LIT_USE_INTERNAL_SHELL")
+if lit_shell_env:
+    use_lit_shell = lit.util.pythonize_bool(lit_shell_env)
+
+config.test_format = toolchain.ShTestLldb(not use_lit_shell)
 
 # suffixes: A list of file extensions to treat as test files. This is overriden
 # by individual lit.local.cfg files in the test subdirectories.