Fix mac build

Small fix for mac build: apple's gcc doesn't comprehend __attribute__((hot))

Change-Id: I2cab22e5bfdc1d22027b12d8103bd56cb407a609
diff --git a/src/base/macros.h b/src/base/macros.h
index 8579872..26f3046 100644
--- a/src/base/macros.h
+++ b/src/base/macros.h
@@ -136,6 +136,12 @@
 #define ALWAYS_INLINE  __attribute__ ((always_inline))
 #endif
 
+#if defined (__APPLE__)
+  #define HOT_ATTR
+#else
+  #define HOT_ATTR __attribute__ ((hot))
+#endif
+
 // bionic and glibc both have TEMP_FAILURE_RETRY, but Mac OS' libc doesn't.
 #ifndef TEMP_FAILURE_RETRY
 #define TEMP_FAILURE_RETRY(exp) ({ \