Currently, `stonith-ng.h` is not allowed to include other Pacemaker headers. This is because dlm includes it.
Prior to dlm v4.2.0, dlm did not have Pacemaker headers along its include path. It included `stonith-ng.h` as `pacemaker/crm/stonith-ng.h`, relative to the default include path. So it fails to build if `stonith-ng.h` includes other Pacemaker headers.
dlm v4.2.0 fixes this (via commit [[ https://pagure.io/dlm/c/5afd9fdc0ef202633f57abc063a5a2c6cef1d61d | 5afd9fd ]]) by using `pkg-config` to add the Pacemaker headers to the include path.
So we need to decide how long we must support dlm versions older than 4.2.0. At that point, we can start including other headers in `stonith-ng.h` and probably simplify some code.
Note that we can't update our include directives inside `stonith-ng.h` to `#include <pacemaker/whatever>` for dlm's sake, because Pacemaker is NOT necessarily installed when we're building Pacemaker. (I tried.) Those includes have to start with `crm/` and be relative to the source tree's `include` directory.