Fix lpstat hanging on IBM AIX

Some macros and functions weren't defined on IBM AIX, define them.

Update CHANGES.md as well with older fixes.

Fixes #773

CHANGES.md

@@ -10,6 +10,8 @@ Changes in CUPS v2.5b1 (TBA)
 - Updated `cupsArray` APIs.
 - Fixed Digest authentication support (Issue #260)
 - Fixed delays in lpd backend (Issue #741)
+- Fixed extensive looping in scheduler (Issue #604)
+- Fixed hanging of `lpstat` on IBM AIX (Issue #773)
 - Fixed segfault in `cupsGetNamedDest()` when trying to get default printer, but
   the default printer is not set (Issue #719)
 - Fixed printing multiple files on specific printers (Issue #643)

cups/request.c

@@ -25,9 +25,11 @@
 #ifndef O_BINARY
 #  define O_BINARY 0
 #endif /* O_BINARY */
-#ifndef MSG_DONTWAIT
+#ifdef _AIX
+#  define MSG_DONTWAIT MSG_NONBLOCK
+#elif !defined(MSG_DONTWAIT)
 #  define MSG_DONTWAIT 0
-#endif /* !MSG_DONTWAIT */
+#endif /* _AIX */
 
 
 /*

scheduler/log.c

@@ -22,6 +22,9 @@
 #  include <systemd/sd-journal.h>
 #endif /* HAVE_ASL_H */
 #include <syslog.h>
+#ifndef va_copy
+#  define va_copy(__list1, __list2) ((void)(__list1 = __list2))
+#endif
 
 
 /*