[BusyBox] bug#1129: sync.c does not compile on RedHat 7.1

[Larry Doolittle]

Odd.  The prototype is
  extern int sync __P ((void));
on both glibc-2.0.7 and 2.1.2 (/usr/include/unistd.h).  The man
page on my system affirms this, tells me "sync always returns 0.",
and claims this conforms to SVr4, SVID, X/OPEN, BSD 4.3.

Which libc does Red Hat 7.1 use?  Is this change a Red Hat
"customization"?  Why was it done?  What does it conform to?
Enquiring minds want to know!

     - Larry Doolittle   <LRDoolittle at lbl.gov>