[dunecontrol,bugfix] Make compiler error during multiarch detection non-fatal again.

The compiler might exit with nonzero exit code if given non-existent
options. Therefore we need to use set +e during this to make dunecontrol
to continue running even the options are not supported.
(cherry picked from commit 28a0a95636db9ac6b9b927a392da8028ea7f0c7f)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>