bridge: Fix build failure with --enable-debug
bridge: Fix build failure with --enable-debug

Fixes

    src/bridge/askpass.c:154:20: error: ‘cockpit_test_signal_backtrace’ undeclared (first use in this function)
      154 |   signal (SIGABRT, cockpit_test_signal_backtrace);

as in debug mode it uses that to set signal handlers.

martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit