Enable guard pages in CHECK_CLIENT

Change the behaviour to use PROT_NONE for reservations in CHECK_CLIENT
mode.  This means that we only provide access once data is actually
being used.

src/ds/defines.h

@@ -114,12 +114,6 @@ namespace snmalloc
 #  endif
 #endif
 
-// // The CHECK_CLIENT macro is used to turn on minimal checking of the client
-// // calling the API correctly.
-// #if !defined(NDEBUG) && !defined(CHECK_CLIENT)
-// #  define CHECK_CLIENT
-// #endif
-
 inline SNMALLOC_FAST_PATH void check_client_error(const char* const str)
 {
   //[[clang::musttail]]
@@ -132,7 +126,7 @@ check_client_impl(bool test, const char* const str)
   if (unlikely(!test))
     check_client_error(str);
 }
-#ifdef CHECK_CLIENT
+#ifdef SNMALLOC_CHECK_CLIENT
 #  define check_client(test, str) check_client_impl(test, str)
 #else
 #  define check_client(test, str)

src/ds/helpers.h

@@ -73,7 +73,7 @@ namespace snmalloc
     }
   };
 
-#ifdef CHECK_CLIENT
+#ifdef SNMALLOC_CHECK_CLIENT
   template<size_t length, typename T>
   class ModArray
   {