Log the exit code of run_apt shell function

It seems like this function sometimes doesn't return non-zero exit code
even though it fails to fetch some packages (e.g. due to a network
error), so log its status code to check if this is really the case.

build/tools/before_install.sh

@@ -17,11 +17,14 @@ case $(uname -s) in
             echo '--- End of APT files dump ---'
 
             run_apt() {
-                echo "Running apt-get $@"
+                echo "-> Running apt-get $@"
 
                 # Disable some (but not all) output.
                 $SUDO apt-get -q -o=Dpkg::Use-Pty=0 "$@"
 
+                echo "-> Done with $?"
+
+                return $?
             }
 
             if [ "$wxUSE_ASAN" = 1 ]; then