[lldb][Shell] Turn detect_container_overflow back off for Shell tests

This environment variable was overridden accidentally in
`b0e130ffe534b05528dccd685a2f2e87af9b2306`. The buildbots
still fail to run the shell-tests without setting this
environment variable to `0` (e.g., https://ci.swift.org/view/LLDB/job/oss-lldb-asan-macos/7709/).
So this patch resumes to old behaviour.

Author: Michael137

lldb/test/Shell/lit.cfg.py

@@ -38,13 +38,6 @@
 # test_exec_root: The root path where tests should be run.
 config.test_exec_root = os.path.join(config.lldb_obj_root, "test", "Shell")
 
-# Begin Swift mod.
-# Swift's libReflection builds without ASAN, which causes a known
-# false positive in std::vector. If sanitizers are off, this is just
-# a no-op
-config.environment['ASAN_OPTIONS'] = 'detect_container_overflow=0'
-# End Swift mod.
-
 # Propagate environment vars.
 llvm_config.with_system_environment(
     [
@@ -58,7 +51,14 @@
 
 # Enable sanitizer runtime flags.
 if "Address" in config.llvm_use_sanitizer:
-    config.environment["ASAN_OPTIONS"] = "detect_stack_use_after_return=1"
+    # Begin Swift mod.
+    # Swift's libReflection builds without ASAN, which causes a known
+    # false positive in std::vector. We also want to support testing a sanitized
+    # lldb using unsanitized llvm, clang, and swift libraries.
+    config.environment[
+        "ASAN_OPTIONS"
+    ] = "detect_container_overflow=0:detect_stack_use_after_return=1"
+    # End Swift mod.
     if platform.system() == "Darwin":
         config.environment["MallocNanoZone"] = "0"