Built-in bzero in GCC 3.0.2

[Eli Zaretskii <eliz at gnu dot org>]

While compiling the readline library in the latest GDB pretest 5.0.92,
GCC 3.0.2 prints numerous warnings like this:

  gcc -c -DHAVE_CONFIG_H   -I. -I. -Id:/usr/djgpp/include
  -DRL_LIBRARY_VERSION='"4.1"' -g -O2 readline.c
  In file included from rldefs.h:53,
                   from readline.c:54:
  d:/usr/djgpp/include/string.h:53: warning: conflicting types for
built-in function `bzero'

(As you see, I used the DJGPP port here.)

The bzero's prototype in DJGPP's string.h is this:

  void * bzero(void *ptr, size_t _len);

Could someone please tell what prototype of bzero does GCC expect?
More generally, how can one know what prototypes does GCC expect from
functions it treats as built-in?

Finally, assuming that modifying the system headers is not an option,
is there any GCC command-line option I can use to avoid this warning?
(I know about -fno-nonansi-builtins, but will older versions of GCC
swallow it without barfing?)

P.S.  Please CC me on your replies, since I don't subscribe to this
list.

TIA