Each unit test can now be run with a separate test binary, making all unit tests more flexible.

* Added feature to compiler test cases with more than one compiler. Added clang as first examples. Fixed test cases to work with gcc

* Added acceptance tests for clang x64, adjusted Travis scripts (now
runs also unittests), install_cross_compilers installs also clang.

* Skips test for cwe415, which is broken on clang + Ubuntu 16.04

* Added feature to compiler test cases with more than one compiler. Added clang as first examples. Fixed test cases to work with gcc

* Added acceptance tests for clang x64, adjusted Travis scripts (now
runs also unittests), install_cross_compilers installs also clang.

* Skips test for cwe415, which is broken on clang + Ubuntu 16.04

* Added change to CHANGES.md

* Fixed test issue: test for json output was pre-compiler suffix.

* Building artificial samples with scons-2, removed makefile

This builds cwe_checker and runs the test suite on Travis CI.