buildgcc: Adapt messages about GNAT and bootstrapping

Don't ask for bootstrapping in case of a different host GCC major
version. GCC's versioning scheme changed starting with the release
of GCC 5. There are no big changes between the versions any more.
Instead, show the message when the host GCC's version is below 4.

In case GNAT can't be found, ask the user to abort and install it.
Also give hints for Ubuntu where the package versions are a little
messy (e.g. the meta packages gcc and gnat often point to different
versions).

In case GNAT is found but is too old (< 4.9), enable bootstrapping
by default and tell the user that building will take longer.

In all three cases show a timeout to draw the user's attention.

v2: Update GNAT check to also look for `gnatbind`. It has to be
    somewhere in $PATH.

Change-Id: I4d9de11d7469e137ede8ad138296d20c0f8ba78f
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/20332
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

0 files changed, 0 insertions, 0 deletions