netbsd: fix build on 6.5

NetBSD 6.5 doesn't have the definition of MAP_ANONYMOUS, so if it
doesn't exist map it to MAP_ANON.

https://mail-index.netbsd.org/tech-userlevel/2014/06/30/msg008646.html
diff --git a/src/common.h.in b/src/common.h.in
index 5d949f3..df1389d 100644
--- a/src/common.h.in
+++ b/src/common.h.in
@@ -53,6 +53,10 @@
 #  endif
 #endif
 
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif /* !MAP_ANONYMOUS */
+
 #define LY_CHECK_GOTO(COND, GOTO) if (COND) {goto GOTO;}
 #define LY_CHECK_ERR_GOTO(COND, ERR, GOTO) if (COND) {ERR; goto GOTO;}
 #define LY_CHECK_RETURN(COND, RETVAL) if (COND) {return RETVAL;}