Reported by Eli Zaretskii <eliz@gnu.org>.
* test-suite/test-suite/lib.scm (%null-device): New variable.
* test-suite/tests/c-api.test (egrep): Use %NULL-DEVICE instead of
/dev/null.
* test-suite/tests/popen.test ("open-input-pipe")["no duplicate"]:
Likewise.
The failure path for the c-api.test had been to call the undefined function
'fail', instead of logging the error like the other tests.
* test-suite/tests/c-api.test: modified
the seek-offset-test. Was just using files that end in "c", but
that caught the new ".doc" files, too, so make sure that files end
in ".c" before requiring that they include unistd.h if they
reference SEEK_(SET|CUR|END).