Move extra size checks behind a config flag.

This will let us turn that flag into a generic "turn on runtime checks" flag
that guards other functionality we have planned.

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -360,7 +360,7 @@
  */
 #undef JEMALLOC_STRERROR_R_RETURNS_CHAR_WITH_GNU_SOURCE
 
-/* Performs additional size-matching sanity checks when defined. */
-#undef JEMALLOC_EXTRA_SIZE_CHECK
+/* Performs additional safety checks when defined. */
+#undef JEMALLOC_OPT_SAFETY_CHECKS
 
 #endif /* JEMALLOC_INTERNAL_DEFS_H_ */

include/jemalloc/internal/jemalloc_preamble.h.in

@@ -161,6 +161,25 @@ static const bool config_log =
     false
 #endif
     ;
+/*
+ * Are extra safety checks enabled; things like checking the size of sized
+ * deallocations, double-frees, etc.
+ */
+static const bool config_opt_safety_checks =
+#if defined(JEMALLOC_EXTRA_SAFETY_CHECKS)
+    true
+#elif defined(JEMALLOC_DEBUG)
+    /*
+     * This lets us only guard safety checks by one flag instead of two; fast
+     * checks can guard solely by config_opt_safety_checks and run in debug mode
+     * too.
+     */
+    true
+#else
+    false
+#endif
+    ;
+
 #if defined(_WIN32) || defined(JEMALLOC_HAVE_SCHED_GETCPU)
 /* Currently percpu_arena depends on sched_getcpu. */
 #define JEMALLOC_PERCPU_ARENA