fix SIGUSR1 signal incompatible windows bug.

[r0ckysec]

xxx.go:64:3: undefined: syscall.SIGUSR1
xxx.go:65:3: undefined: syscall.SIGUSR2
xxx.go:68:3: undefined: syscall.SIGTSTP
xxx.go:111:5: undefined: syscall.SIGUSR1
xxx.go:112:5: undefined: syscall.SIGUSR2
xxx.go:115:5: undefined: syscall.SIGTSTP
xxx.go:119:5: undefined: syscall.SIGUSR1
xxx.go:120:5: undefined: syscall.SIGUSR2
xxx.go:123:5: undefined: syscall.SIGTSTP
xxx.go:224:3: undefined: syscall.Kill
xxx.go:224:3: too many errors

after fixing, it can be compiled normally

The items in question are: fvbock/endless#30

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[wizardishungry]

Should this have been approved? The CL has comments not addressed & the patch includes an implementation of Kill that silently does nothing, which is very different from what the JS implementation does. cc @ianlancetaylor

(Edit: I think I got confused because it seems Github lets anyone approve PRs but only people with write access can merge them?)