ODR violation in unittest binary

[margnus1]

Linking object object files compiled with RTTI with object files compiled without RTTI leads to violations of the one definition rule, something that GCC 8 has started warning about when compiling with LTO:

../../src/vecset.h:32:25: warning: virtual table of type ‘struct VecSet’ violates one definition rule [-Wodr]
template<class T> class VecSet{
                        ^
../../src/vecset.h:32:25: note: the conflicting type defined in another translation unit has virtual table with more entries

Newer versions of boost unit test does not require RTTI, but the oldest one we currently support does; otherwise compiling unittest without RTTI would be the obvious solution.