Run C/shell API tests in CI

[pevik]

trafficstars

We have bunch of tests in lib/newlib_tests/ (both C and shell), which we want to run. The best would be to have make test target + simple scripts which handles tests.

First version has been sent, but needs some improvements https://patchwork.ozlabs.org/patch/1166785/

This helps to run tests in travis.

UPDATE: we agreed on make test{,-c,-shell} targets. make check are used for static analysis patch (https://patchwork.ozlabs.org/project/ltp/list/?series=253430).

Related to #312.

[pevik]

Patchset sent: https://patchwork.ozlabs.org/project/ltp/list/?series=253501

[pevik]

Already implemented long time ago (although improvements could be done).