darwin: fix ios build error

Include <errno.h> and <stdlib.h>.  They're being pulled in implicitly
on OS X but apparently that's not the case with iOS builds.

Build breakage introduced in 5ff6f85 by yours truly. Mea culpa.

Fixes #885 and #891.
darwin: fix ios compiler warning

uv__fsevents_loop_delete() returns void. Remove the 'return 0'
statement.