BUILD: ssl: use MAP_ANON instead of MAP_ANONYMOUS

FreeBSD uses the former, Linux uses the latter but generally also
defines the former as an alias of the latter. Just checked on other
OSes and AIX defines both. So better use MAP_ANON which seems to be
more commonly defined.
diff --git a/src/shctx.c b/src/shctx.c
index c6c6737..48d9541 100644
--- a/src/shctx.c
+++ b/src/shctx.c
@@ -372,7 +372,7 @@
 		size = SHCTX_DEFAULT_SIZE;
 
 	shctx = (struct shared_context *)mmap(NULL, sizeof(struct shared_context)+(size*sizeof(struct shared_session)),
-	                                      PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+	                                      PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
 	if (!shctx || shctx == MAP_FAILED) {
 		shctx = NULL;
 		return -1;