fix build on darwin.

Change-Id: I655b92f0a09bc4bc1b2b277b24ca24c081b4da94
diff --git a/libacc/acc.cpp b/libacc/acc.cpp
index 73d2cdd..6e13f9a 100644
--- a/libacc/acc.cpp
+++ b/libacc/acc.cpp
@@ -25,6 +25,10 @@
 
 #include <sys/mman.h>
 
+#if defined(MAP_ANON) && !defined(MAP_ANONYMOUS)
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+
 #if defined(__arm__)
 #define DEFAULT_ARM_CODEGEN
 #define PROVIDE_ARM_CODEGEN