os: implement StartProcess

Signed-off-by: leongross <leon.gross@9elements.com>

src/syscall/syscall_libc.go

@@ -233,6 +233,11 @@ func (w WaitStatus) Continued() bool    { return false }
 func (w WaitStatus) StopSignal() Signal { return 0 }
 func (w WaitStatus) TrapCause() int     { return 0 }
 
+// since rusage is quite a big struct and we stub it out anyway no need to define it here
+func Wait4(pid int, wstatus *WaitStatus, options int, rusage uintptr) (wpid int, err error) {
+	return 0, ENOSYS // TODO
+}
+
 func Getenv(key string) (value string, found bool) {
 	data := cstring(key)
 	raw := libc_getenv(&data[0])

src/syscall/syscall_unix.go

@@ -1,3 +1,5 @@
+//go:build linux || unix
+
 package syscall
 
 func Exec(argv0 string, argv []string, envv []string) (err error)