Clarify and deduplicate string comment

Author: ldionne

libcxx/include/string

@@ -680,14 +680,12 @@ _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.
+// Within the <string> implementation, use `_LIBCPP_ENABLE_ASAN_CONTAINER_CHECKS_FOR_STRING`
+// to determine whether ASAN container checks should be provided.
 //
-// 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,
+// The _LIBCPP_STRING_INTERNAL_MEMORY_ACCESS macro disables 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,
 // such as unused bytes in short strings, that should never be accessed by other parts of the program.
 #  if _LIBCPP_ENABLE_ASAN_CONTAINER_CHECKS && _LIBCPP_INSTRUMENTED_WITH_ASAN
 #    define _LIBCPP_ENABLE_ASAN_CONTAINER_CHECKS_FOR_STRING 1