buildroot

uclibc: update internal toolchain build

Update the uClibc build procedure to accomodate for the new build
system, otherwise it breaks with snapshot versions.
As pointed by linuxjacques on IRC.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>