Fix the RealtimeKit dbus include guards

The SDL_USE_LIBDBUS define is set inside SDL_debug.h, therefore the
circular dependency made it impossible for this feature to be enabled.

Instead, guard SDL_dbus.h based on the autoconf variable HAVE_DBUS_DBUS_H

Additionally, fix one of the rtkit comments. CAP_SYS_NICE isn't required
to achieve high priority. But there is some scheduler config that rtkit
needs the app to setup.
2 files changed