Remove unistd.h import breaking Windows build (#59)
Remove unistd.h import breaking Windows build (#59)

Remove unistd.h import breaking Windows build and replace use of POSIX _exit with C standard library exit (to remove the need for unistd.h).
dloeng/guetzli,guanzidashu/guetzli_ios_metal,szabadka/guetzli,szabadka/guetzli,guanzidashu/guetzli_ios_metal,guanzidashu/guetzli_ios_metal,guanzidashu/guetzli_ios_metal,google/guetzli,google/guetzli,ianhuang-777/guetzli,ianhuang-777/guetzli,ianhuang-777/guetzli,dloeng/guetzli,szabadka/guetzli,dloeng/guetzli,ianhuang-777/guetzli,google/guetzli,google/guetzli