Move Swift modification to a place where it is not a noop

Author: adrian-prantl

lldb/test/Unit/lit.cfg.py

@@ -14,13 +14,6 @@
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = []
 
-# 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'
-# End Swift mod.
-
 # test_source_root: The root path where unit test binaries are located.
 # test_exec_root: The root path where tests should be run.
 config.test_source_root = os.path.join(config.lldb_obj_root, "unittests")
@@ -45,5 +38,13 @@
 config.environment["ASAN_OPTIONS"] = "detect_stack_use_after_return=1"
 config.environment["TSAN_OPTIONS"] = "halt_on_error=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'
+# End Swift mod.
+
+
 # testFormat: The test format to use to interpret tests.
 config.test_format = lit.formats.GoogleTest(config.llvm_build_mode, "Tests")