cygwin: fix undefined _SC_PAGESIZE
cygwin: fix undefined _SC_PAGESIZE

unistd.h was not included, when tried to build node 0.5.9 had an error of:
_SC_PAGESIZE undefined

unknownbrackets/maxcso,urbit/archaeology2,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso