Fixing compilation and tests for GCC on Linux

* Compilation using GCC (4.8.2) on my platform (Archlinux) throws some errors. Provided changes are simple way to fix this issue (additional flag in Makefile and ```_BSD_SOURCE``` definition) .
* Also there is a problem with tests when using GCC. Several tests of NMEA frames fail at memcmp. It looks like some elements are not properly initialized in ```expected``` structs (bool type variables) - there is some random data left. Simple fix is to declare them static, so they are automatically zeroed before initialization.