- fix missing initializer for member [-Werror=missing-field-initializers]
- fix ISO C++ forbids casting between pointer-to-function and pointer-to-object [-Werror=pedantic]
- add gcc-4.8 tests
- ubuntu has less patches than CentOS7 on gcc, some old bugs are not
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55971
- https://sourceware.org/bugzilla/show_bug.cgi?id=25399
- compat.cmake
- disable some features with old compilers
