games/aquaria: unbreak after r443975

Aquaria/Continuity.cpp:(.text+0x1684e): undefined reference to `tinyxml2::StrPair::GetStr()'
CMakeFiles/aquaria.dir/Aquaria/DSQ.cpp.o: In function `DSQ::loadModsCallback(std::1::basic_string<char, std::1::char_traits<char>, std::__1::allocator<char> > const&, long)':
Aquaria/DSQ.cpp:(.text+0x1014e): undefined reference to `tinyxml2::StrPair::GetStr()'
c++: error: linker command failed with exit code 1 (use -v to see invocation)

Reported by: pkg-fallout