Revert "toolchain-internal: skip gcc-intermediate when possible"

While the idea of skipping the intermediate gcc step seems to work
fine in most situations, it causes problems with the SSP
support. Until we can figure out a proper solution for this problem,
we need to revert back to the previous solution of a three stages
build.

This reverts commit 2babed4a.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>