Issue #2510 has been updated by Usaku NAKAMURA.


additional information:

to invoke native Windows child processes, xsystem returns true,
but there is no output in mkmf.log except the names of invoked
processes.

to invoke cygwin processes, xsystem returns false.

I think that ruby destroys stdout.
And, starting of processes might fail for such case in cygwin. 
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http://redmine.ruby-lang.org/issues/show/2510

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