Under FreeBSD, /usr/include/sys/mman.h does not include /usr/include/sys/types.h. The OpenSSH test for anonymous shared memory maps includes mman.h without including types.h and the test code snippet compile fails. I'll report the omission to the FreeBSD folks, but changing the snippet in configure to include <sys/types.h> will allow FreeBSD folks to use compression and privilege separation until then.
*** This bug has been marked as a duplicate of 303 ***
already solve in CVS tree