ktrace does not show proper return values for pipe(2)

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

When ktracing a pipe syscall, the output is:

57705 a.out    CALL  pipe
57705 a.out    RET   pipe 3

However, the return value of pipe is 0, and the returned value for the 
file descs is {3, 4}.

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