Silence compiler warnings for unreachable code.

Reported by Ingvar Hagelund.
diff --git a/include/jemalloc/internal/arena.h b/include/jemalloc/internal/arena.h
index 62a9a85..f2954b3 100644
--- a/include/jemalloc/internal/arena.h
+++ b/include/jemalloc/internal/arena.h
@@ -659,12 +659,13 @@
 {
 	size_t size;
 
-	if (CHUNK_MAP_SIZE_SHIFT > 0)
-		size = (mapbits & CHUNK_MAP_SIZE_MASK) >> CHUNK_MAP_SIZE_SHIFT;
-	else if (CHUNK_MAP_SIZE_SHIFT == 0)
-		size = mapbits & CHUNK_MAP_SIZE_MASK;
-	else
-		size = (mapbits & CHUNK_MAP_SIZE_MASK) << -CHUNK_MAP_SIZE_SHIFT;
+#if CHUNK_MAP_SIZE_SHIFT > 0
+	size = (mapbits & CHUNK_MAP_SIZE_MASK) >> CHUNK_MAP_SIZE_SHIFT;
+#elif CHUNK_MAP_SIZE_SHIFT == 0
+	size = mapbits & CHUNK_MAP_SIZE_MASK;
+#else
+	size = (mapbits & CHUNK_MAP_SIZE_MASK) << -CHUNK_MAP_SIZE_SHIFT;
+#endif
 
 	return (size);
 }
@@ -776,12 +777,13 @@
 {
 	size_t mapbits;
 
-	if (CHUNK_MAP_SIZE_SHIFT > 0)
-		mapbits = size << CHUNK_MAP_SIZE_SHIFT;
-	else if (CHUNK_MAP_SIZE_SHIFT == 0)
-		mapbits = size;
-	else
-		mapbits = size >> -CHUNK_MAP_SIZE_SHIFT;
+#if CHUNK_MAP_SIZE_SHIFT > 0
+	mapbits = size << CHUNK_MAP_SIZE_SHIFT;
+#elif CHUNK_MAP_SIZE_SHIFT == 0
+	mapbits = size;
+#else
+	mapbits = size >> -CHUNK_MAP_SIZE_SHIFT;
+#endif
 
 	assert((mapbits & ~CHUNK_MAP_SIZE_MASK) == 0);
 	return (mapbits);