sanitise: some flags are missing for ubsan

The flag -fsanitize=undefined enables most checks, but not all. Clang has some additional groups depending on the version that enable everything else. GCC has no groups and enabling every single option individually is very error-prone between versions.

http://releases.llvm.org/6.0.0/tools/clang/docs/UndefinedBehaviorSanitizer.html

http://releases.llvm.org/7.0.0/tools/clang/docs/UndefinedBehaviorSanitizer.html

http://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html

@melvin has something prepared.