Explicit linking against -lstdc++ disqualifies clang w/ libc++

[mgorny]

vtable-dumper is explicitly linking to -lstdc++ used to provide __cxa_demangle(). However, libstdc++ is only valid for gcc (and clang with gcc libstdc++). The other compilers provide __cxa_demangle() in other libraries. For example, clang in GNU-free environment uses -lc++ (well, the needed symbol is actually often provided by -lc++abi or -lcxxrt sub-library), in which case -lstdc++ is either going to be wrong (i.e. force dependency on wrong C++ library on system using purely clang suite) or fail (when there is no gcc).

To be honest, I really don't see a point in building vtable-dumper as C if it requires the C++ library anyway. Therefore, the simplest solution to the problem would be to build it using a C++ compiler which in turn will use the correct C++ library for the ecosystem used (and also guarantee correct ABI for __cxa_demangle() calls — it would also be more correct to #include <cxxabi.h> instead of redeclaring the function).