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-4.2.1.orig/libstdc++-v3/configure gcc-4.2.1/libstdc++-v3/configure

 --- gcc-4.2.1.orig/libstdc++-v3/configure	2007-08-03 20:30:21.000000000 +0200

 +++ gcc-4.2.1/libstdc++-v3/configure	2007-08-03 20:33:56.000000000 +0200

 @@ -7514,6 +7514,9 @@

  cat >>conftest.$ac_ext <<_ACEOF

  /* end confdefs.h.  */

  #include <complex.h>

 +#ifdef __UCLIBC__

 +#error ugly hack to make sure configure test fails here for cross until uClibc supports the complex funcs

 +#endif

  int

  main ()

  {