Preprocessor macro should check value of variable, not only if is defined
Fix build GNU/kfreebsd

 - check if cpu_set_t is available
 - only typedef if it's not
 - Check for __FREEBSD__ instead of __FreeBSD__
configure.ac - test if folders exist before we include them
Revert "Preprocessor macro should check value of variable, not only if is defined"

This reverts commit 741dbe72ad10dd330090b892b58fc6fc2b3e6f7d.
cpu_set_t is defined in sched.h No need to include sys/cpuset.h
[Coding style] improve wording in doxygen comments
Unify preprocessor checks
Merge remote-tracking branch 'upstream/GNU/kFreeBSD' into up-next

Conflicts:
	src/fg_affinity.c