AIX-specific addition for /sys/src/cmd/unix/u9fs/plan9.h

Tested with xlc on AIX4.3, AIX5.1 and gcc on AIX5.1.
Also compiles — with few warnings — on AIX5.3 and AIX6.1.

Notes:
Fri Mar 25 17:14:24 EDT 2011 geoff
    We try to keep ifdefs out of our code.
    Perhaps you should add it to your copy of fcall.h on Unix.


Reference: /n/sources/patch/sorry/u9fs-aix
Date: Thu Mar 24 17:18:28 CET 2011
Signed-off-by: yarikos@gmail.com
Reviewed-by: geoff

--- /sys/src/cmd/unix/u9fs/plan9.h	Thu Mar 24 17:13:12 2011
+++ /sys/src/cmd/unix/u9fs/plan9.h	Thu Mar 24 17:13:09 2011
@@ -24,6 +24,9 @@
 #endif /* IRIX5X */
 #endif /* sgi */
 
+#ifdef _AIX
+#pragma enum(small)	/* for fcall.h:/NOFID/ */
+#endif /* _AIX */
 
 #ifdef sun	/* sparc and __svr4__ are also defined on the offending machine */
 #define __EXTENSIONS__	1	/* for struct timeval */