Add comment about disablement not being honored in string

Author: ldionne

libcxx/include/string

@@ -681,6 +681,10 @@ _LIBCPP_PUSH_MACROS
 // Since std::string is partially instantiated in the built library, we require that the library
 // has been built with ASAN support in order to enable the container checks in std::string.
 //
+// This also means that if the built library has been compiled with sanitizer checks enabled
+// and the user requests for the container checks to be disabled, that request will not be
+// honored.
+//
 // The _LIBCPP_STRING_INTERNAL_MEMORY_ACCESS macro disables AddressSanitizer (ASan) instrumentation
 // for a specific function, allowing memory accesses that would normally trigger ASan errors to proceed
 // without crashing. This is useful for accessing parts of objects memory, which should not be accessed,