This replaces header include guards with `#pragma once`.
A couple of include guards are not removed yet (e.g. `__RNA_TYPES_H__`),
because they are used in other places.
This patch has been generated by P1561 followed by `make format`.
Differential Revision: https://developer.blender.org/D8466
Adds a check when starting blender if your platform is supported. We use a blacklist
as drivers are updated more regular then blender (stable releases).
The mechanism detects if the support level changed or has been validated by the user previously.
Changes can happen due to users updating their drivers, but also when we change the support
level in our code base.
When the user has seen the limited support level message it is saved in the user config.
It would be better to have a system specific config section, but currently not clear
what could benefit from that.
When the platform is unsupported or has limited support a dialog box will appear including a link
to our user manual describing what to do.
**Windows**
Windows uses the MessageBox that is provided by the windows kernel.
**X11**
We use a very lowlevel messagebox for X11. It is very limited in use and can be fine tuned when needed.
**SDL/APPLE**
There is no implementation for SDL or APPLE at this moment as the platform support feature targets mostly Windows users.
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D5955
