libc/glibc: add fortify option

By default, recent versions of glibc and eglibc will build some
functions that take format strings (eg. printf, syslog...) with
run-time checks against some format string attacks. This is
called a fortified build.

Unfortunately, this fails somehow while building the instrumented
version of syslog, with some kind of circular dependency...

Disable fortified builds by default, and hide the enabling option
behind EXPERIMENTAL for daring users...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

2008-04-28  Hiroki Kaminaga  <kaminaga@sm.sony.co.jp>

	[BZ 6740]

	nptl/sysdeps/powerpc/tcb-offsets.sym (PRIVATE_FUTEX_OFFSET):

	Guard sym definition with #ifndef __ASSUME_PRIVATE_FUTEX.

--- a/nptl/sysdeps/powerpc/tcb-offsets.sym

+++ b/nptl/sysdeps/powerpc/tcb-offsets.sym

@@ -15,4 +15,6 @@

 PID				thread_offsetof (pid)

 TID				thread_offsetof (tid)

 POINTER_GUARD			(offsetof (tcbhead_t, pointer_guard) - TLS_TCB_OFFSET - sizeof (tcbhead_t))

+#ifndef __ASSUME_PRIVATE_FUTEX

 PRIVATE_FUTEX_OFFSET		thread_offsetof (header.private_futex)

+#endif