Prefer system-wide toolchain, over local prebuilt one.

Signed-off-by: Dmitrijs Ledkovs <dmitrijs.ledkovs@canonical.com>
Signed-off-by: Sergio Schvezov <sergio.schvezov@canonical.com>
Merge commit 'b141885cff001404c4a35d495a76bcad35603c63' into phablet-10.1