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>

 diff -durN gcc-3.4.6.orig/gcc/config/mips/t-linux gcc-3.4.6/gcc/config/mips/t-linux

 --- gcc-3.4.6.orig/gcc/config/mips/t-linux	1970-01-01 01:00:00.000000000 +0100

 +++ gcc-3.4.6/gcc/config/mips/t-linux	2007-08-15 23:08:15.000000000 +0200

 @@ -0,0 +1,3 @@

 +# Compile crtbegin/end with xgot so it works for both

 +# normal and large GOTs.

 +CRTSTUFF_T_CFLAGS = -mxgot