[uClibc] buildroot cross-compilation target system image

[Ondra]

With cross-compilation target system image I mean, that the image at the 
end of the process whould have beed a LFS root, that has the binutils, 
gcc and some other packages in, but can also be set to cross-compile, 
while I still can chroot to it.

The present buildroot can only build the native toolchain inside the 
target system image (or if I'm wrong ... sorry then).