updated for version 7.4.055
Problem: Mac: Where availability macros are defined depends on the system.
Solution: Add a configure check. (Felix Bünemann)
diff --git a/src/config.h.in b/src/config.h.in
index 422fd1f..a4e216b 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -442,3 +442,6 @@
/* Define if you want Cygwin to use the WIN32 clipboard, not compatible with X11*/
#undef FEAT_CYGWIN_WIN32_CLIPBOARD
+
+/* Define if we have AvailabilityMacros.h on Mac OS X */
+#undef HAVE_AVAILABILITYMACROS_H