MFC r274040 and r274084.  The result is removal of agp_intel.c from
the static amd64 kernel when agp is configured.
MFC r274023:
When other end of the pipe closed during the write, but some bytes
were written, return short write instead of EPIPE.
MFC r274343:
When sleeping waiting for the profiling stop, always set P_STOPPROF
before dropping process lock.  Clear P_STOPPROF when doing wakeup.