Seems they've never seen gcc on AIX.

--- cshim/mqbasictypes.h.orig	2010-03-01 18:00:38 +0100
+++ cshim/mqbasictypes.h	2010-03-01 18:00:58 +0100
@@ -64,7 +64,7 @@
 #endif
 #endif
 
-#if (defined(__IBMC__) || defined (__IBMCPP__)) && defined(__unix__)
+#if ((defined(__IBMC__) || defined (__IBMCPP__)) && defined(__unix__)) || defined(_AIX)
 #ifndef AIX 
 #define AIX 
 #endif