Build uClibc toolchain with Buildroot

Signed-off-by: Anton Kolesov <anton.kolesov@synopsys.com>
Support testing of toolchain built by Buildroot

Signed-off-by: Anton Kolesov <anton.kolesov@synopsys.com>
Support new toolchain option in kernel build

Signed-off-by: Anton Kolesov <anton.kolesov@synopsys.com>