travis: check kernel as part of travis testing.

add 2 more jobs (one for gcc, one for clang) which only compile Cppcheck with opimization CXXFLAGS to afterwards check a fixed version of the linux kernel to see if cppcheck crashes.
Merge pull request #266 from matthiaskrgr/travis

travis: check kernel as part of travis testing.
Fixed crash on wrong __attribute__((constructor)) syntax
Fixed #3852: Support simplification of C++11 "enum class", fixed existing simplifications
Refactor signal handling code: prepare for demangling names, handle SIGINT w/o backtrace, remove our own signal handler frames from backtrace
Merge branch 'master' of https://github.com/danmar/cppcheck
Fixed #4928 (C++ operator aliases result in false 'assigned a value that is never used' warning)
Fixed #4804 (Improve check for 'std::string::data()' - identical to 'std::string::c_str()')
Extended std.cfg about <cstring> functions and added testcases.
Astyle running and added test cases for functions in std.cfg.
travis: remove HAVE_RULES=yes-only build. If we dealing with a clang job, abort the kernel checking, so we have basically only one compiler checking the kernel with cppcheck which should be enough.
Fixed #5481: std::array is POD, so using memcpy (etc.) is allowed on it.
Merge pull request #267 from matthiaskrgr/travis

travis: remove HAVE_RULES=yes-only build and dublicted kernel checking