syscall: allow for mksyscall_windows.pl to be used outside of syscall
syscall: allow for mksyscall_windows.pl to be used outside of syscall

this change should have been part of fafcd328da73

R=golang-dev, bsiegert
CC=golang-dev
http://codereview.appspot.com/5462045

wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old