Refactor checks to improve codegen.

src/mem/allocconfig.h

@@ -8,6 +8,22 @@ namespace snmalloc
 // calling the API correctly.
 #if !defined(NDEBUG) && !defined(CHECK_CLIENT)
 #  define CHECK_CLIENT
+#endif
+
+  SNMALLOC_FAST_PATH void check_client_impl(bool test, const char* const str)
+  {
+#ifdef CHECK_CLIENT
+    if (unlikely(!test))
+      error(str);
+#else
+    UNUSED(test);
+    UNUSED(str);
+#endif
+  }
+#ifdef CHECK_CLIENT
+#  define check_client(test, str) check_client_impl(test, str)
+#else
+#  define check_client(test, str)
 #endif
 
   // 0 intermediate bits results in power of 2 small allocs. 1 intermediate