[CentOS] Problem with gettid() on CentOS 5/gcc 4.1.1

> What packages do you need installed?

On a CentOS 4.4 system I get the following:

   # rpm -qf /usr/include/linux/unistd.h
   glibc-kernheaders-2.4-9.1.98.EL

and

   # grep -RE "#define[[:space:]]+_syscall" /usr/include
   /usr/include/linux/unistd.h:#define _syscall0(type,name) \
   /usr/include/linux/unistd.h:#define _syscall1(type,name,type1,arg1) \
   /usr/include/linux/unistd.h:#define _syscall2 
(type,name,type1,arg1,type2,arg2) \
   /usr/include/linux/unistd.h:#define _syscall3 
(type,name,type1,arg1,type2,arg2,type3,arg3) \
   /usr/include/linux/unistd.h:#define _syscall4 
(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4) \
   /usr/include/linux/unistd.h:#define _syscall5 
(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4, \
   /usr/include/linux/unistd.h:#define _syscall6 
(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4, \

So the macros are being defined as expected, but not on my CentOS 5  
beta system (then again, it is just a beta, but this file shouldn't  
change very often).

Alfred