tests: don't risk hanging on the 'cl' requirement On the GNU/Linux boxes of some users that run our testsuite there is a '/usr/local/bin/cl' executable, from the IRAF package: <http://iraf.noao.edu/> The test 'compile4.sh' (and other tests) try to invoke the 'cl' command to check whether it's a Microsoft compiler; the IRAF cl is an interactive program, so it hangs on such invocation. In conclusion, the testsuite hangs for those users which have the IRAF cl early in PATH. Fix the issue by redirecting the input of cl from /dev/null when invoking it, which is enough to prevent the cl program from IRAF from hanging, and should have no effect on the behaviour of the Microsoft compiler. This change fixes automake bug#14707. * t/ax/am-test-lib.sh (require_tool): Adjust the handling of the 'cl' requirement. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>