[compiler-rt] Default to Lit's Internal Shell

All of the tests should work with the internal shell now, at least on
x86 Linux. Enable it by default for the performance/debuggability
advantages.

Reviewers: vitalybuka, fmayer

Reviewed By: fmayer, vitalybuka

Pull Request: #165148

Author: boomanaiden154

compiler-rt/test/lit.common.cfg.py

@@ -113,12 +113,17 @@ def push_dynamic_library_lookup_path(config, new_path):
         config.environment[dynamic_library_lookup_var] = new_ld_library_path_64
 
 
+# TODO: Consolidate the logic for turning on the internal shell by default for all LLVM test suites.
+# See https://github.com/llvm/llvm-project/issues/106636 for more details.
+#
 # Choose between lit's internal shell pipeline runner and a real shell.  If
 # LIT_USE_INTERNAL_SHELL is in the environment, we use that as an override.
-use_lit_shell = os.environ.get("LIT_USE_INTERNAL_SHELL")
+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)
 if use_lit_shell:
-    # 0 is external, "" is default, and everything else is internal.
-    execute_external = use_lit_shell == "0"
+    execute_external = True
 else:
     # Otherwise we default to internal on Windows and external elsewhere, as
     # bash on Windows is usually very slow.