toolchain/crosstool-NG: fix up ct-ng config file to saner defaults

Peter on IRC reported some build failures for different targets.
They were of two kinds:
 - missing/unknown stack unwinding support
 - missing *_chk functions

The first is about configure not being able to automagically determine
if stack unwinding support is available for the target. The second is
about fortified build forgetting to build the fortified functions.
This applies to both glibc and eglibc.

After some discussions on IRC with Jacmet, it appears that we can
safely assume both of the following:
 - virtually all targets of buildroot will have stack unwinding support
 - we do not care about fortified builds (so far)

So, update the bundled crosstool-NG .config file to saner defaults:
 - force unwind support
 - disable fortified builds

[Peter: fix 'force non-fortified build' sed invocation]
Reported-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>