Require that ldc and ldc-runtime are of the same version
Right now it's possible to have ldc 1.19.0 and ldc-runtime 1.18.0 installed, e.g. if something depends on the shared library of ldc-runtime 1.18.0 and hasn't been rebuilt. It'd be nice if there was a version requirement for ldc-runtime (or from ldc-runtime on ldc) so that this can't happen since stuff breaks horribly when mixing different versions of ldc-runtime and ldc.