Quoting error message to avoid warnings

Author: gershnik

lib/inc/sys_string/config.h

@@ -126,7 +126,7 @@
 #elif defined(_LIBCPP_VERSION)
     #if _LIBCPP_VERSION >= 13000 && _LIBCPP_VERSION < 160000 && defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
         #if defined(_LIBCPP_RANGES) || defined(_LIBCPP_ITERATOR)
-            #error Your very old libc++ doesn't automatically enable ranges. To work around it include sys_string headers *before* <ranges> or <iterator>
+            #error "Your very old libc++ doesn't automatically enable ranges. To work around it include sys_string headers *before* <ranges> or <iterator>"
         #endif
 
         #undef _LIBCPP_HAS_NO_INCOMPLETE_RANGES