[Xenomai] Error "field ‘pse51_si’ has incomplete type" in syscall.h after upgrading Ubuntu Distrib to 13.04

[Marc Le Douarain <marc.le-douarain@laposte.net>]

Hello everybody,

I have an application using Xenomai that do no more compile after I have 
recently upgraded from Ubuntu 12.10 to 13.04

Here the error I have in one one file including "phread.h" :
gcc -c tasks.c -o tasks.o -march=i486 ...(custom defines)... 
`xeno-config --skin posix --cflags`
In file included from /usr/xenomai/include/asm/xenomai/syscall.h:23:0,
                  from /usr/xenomai/include/nucleus/trace.h:52,
                  from /usr/xenomai/include/nucleus/system.h:27,
                  from /usr/xenomai/include/asm/xenomai/system_32.h:137,
                  from /usr/xenomai/include/asm/xenomai/system.h:2,
                  from /usr/xenomai/include/nucleus/types.h:41,
                  from /usr/xenomai/include/nucleus/thread.h:25,
                  from /usr/xenomai/include/posix/pthread.h:136,
                  from tasks.c:34:
/usr/xenomai/include/asm-generic/xenomai/syscall.h:78:17: erreur: field 
‘pse51_si’ has incomplete type
make: *** [tasks.o] Erreur 1

gcc installed on this version is 4.7.3
My project based on Linux kernel 2.6.38.8 and Xenomai 2.5.6

any one have an idea, on something that could be done...?
else I'm thinking to install an older version in virtual machine to no 
more encounter bad surprises with upgrades !

Many thanks in advance.