Use non-strict-ansi mode to build sources

The sources don't allow to be build in strict ansi mode. Thus the change from GNU++11 mode to C++11 in 6a46ad138c02138bb8f9a425afdec149bfa39182 made building the sources impossible. This was also catched by Travis CI but ignored by the author and merged anyway.

Revert this change until the source can be compiled in strict ansi mode and Travis CI support C++11.