- No need to use a PCH when compiling a 1-file library.
- Add the _NTSYSTEM_ definition.
- Since the arbiter.h file is to be included by the users of this
library, namely only kernel-mode NT components (incl. NTOS), there
is no need to include the standard kernel-mode headers in it.
Include these headers instead in the private implementation of the
library, arbiter.c.