assert: fix missing function in NDEBUG mode

include/bits/assert.hpp

@@ -97,6 +97,8 @@ fail_fast(const char* type,
 #define bits_expects(cond)
 #define bits_ensures(cond)
 #define bits_assert(cond)
+#define bits_return_val_if_fail(cond, val)
+#define bits_return_if_fail(cond)
 #else
 #define bits_expects(cond) BITS_CONTRACT_CHECK("Precondition", cond)
 #define bits_ensures(cond) BITS_CONTRACT_CHECK("Postcondition", cond)
@@ -107,7 +109,6 @@ fail_fast(const char* type,
 
 #define bits_return_if_fail(cond)                                             \
     BITS_CONTRACT_CHECK_RETURN("Precondition", cond)
-
 #endif
 
 #endif