buildroot

toolchain-external/Config.in: fix indentation

Fix the indentation of the external toolchain Config file, where tabs
and spaces are mixed as indentation even within the same block.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>