Compiling errors on RedHat 5.1

I am using a i386 machine with RedHat 5.1 installed.

Trying to recompile the 6.3.2 version of PostgreSQL I found the
following errors :

gcc -I../../../include -I../../../backend -Wall -Wmissing-prototypes
-I../.. -c ipc.c -o ipc.o
In file included from /usr/include/sys/sem.h:31,
from ipc.c:38:
/usr/include/sys/sem_buf.h:57: redefinition of `union semun'
make[3]: *** [ipc.o] Error 1

and also

gcc -I../../../include -I../../../backend -Wall -Wmissing-prototypes
-I../.. -c proc.c -o proc.o
In file included from /usr/include/sys/sem.h:31,
from proc.c:71:
/usr/include/sys/sem_buf.h:57: redefinition of `union semun'
make[3]: *** [proc.o] Error 1

From that point, the compilation was aborted.

Any clues ?

Please cc: me directly to teo@flex.ro

--
Constantin Teodorescu
FLEX Consulting Braila, ROMANIA