convert all to use sys/linux over sys/unix; new implementations for pipe, process and env

core/os/os2/pipe_linux.odin

@@ -1,7 +1,17 @@
 //+private
 package os2
 
+import "core:sys/linux"
+
 _pipe :: proc() -> (r, w: ^File, err: Error) {
-	return nil, nil, nil
+	fds: [2]linux.Fd
+	errno := linux.pipe2(&fds, {.CLOEXEC})
+	if errno != .NONE {
+		return nil, nil,_get_platform_error(errno)
+	}
+
+	r = _new_file(uintptr(fds[0]))
+	w = _new_file(uintptr(fds[1]))
+	return
 }