[atomic] Cannot fail anymore

src/hb-atomic.hh

diff --git a/src/hb-atomic.hh b/src/hb-atomic.hh
index 93265f6..e640d1b 100644
--- a/src/hb-atomic.hh
+++ b/src/hb-atomic.hh
@@ -102,20 +102,12 @@
 #define hb_atomic_ptr_impl_cmpexch(P,O,N)	_hb_atomic_ptr_impl_cmplexch ((const void **) (P), (O), (N))
 
 
-#elif defined(HB_NO_MT)
+#else /* defined(HB_NO_MT) */
 
 #define hb_atomic_int_impl_add(AI, V)		((*(AI) += (V)) - (V))
-
 #define _hb_memory_barrier()			do {} while (0)
-
 #define hb_atomic_ptr_impl_cmpexch(P,O,N)	(* (void **) (P) == (void *) (O) ? (* (void **) (P) = (void *) (N), true) : false)
 
-
-#else
-
-#error "Could not find any system to define atomic_int macros."
-#error "Check hb-atomic.hh for possible resolutions."
-
 #endif