MINOR: compiler: restore the likely() wrapper for gcc 5.x
After some tests, gcc 5.x produces better code with likely()
than without, contrary to gcc 4.x where it was better to disable
it. Let's re-enable it for 5 and above.
diff --git a/include/common/compiler.h b/include/common/compiler.h
index 001b893..ee7744c 100644
--- a/include/common/compiler.h
+++ b/include/common/compiler.h
@@ -89,8 +89,8 @@
#define __builtin_expect(x,y) (x)
#define likely(x) (x)
#define unlikely(x) (x)
-#elif __GNUC__ < 4
-/* gcc 3.x does the best job at this */
+#elif __GNUC__ < 4 || __GNUC__ >= 5
+/* gcc 3.x and 5.x do the best job at this */
#define likely(x) (__builtin_expect((x) != 0, 1))
#define unlikely(x) (__builtin_expect((x) != 0, 0))
#else