fix: remove static libstdc++ linking on Linux to prevent potential crashes

[xfxdev]

fix #1079

Unity on Linux is dynamically linked against the system's libstdc++.so. Statically linking libstdc++ in a native plugin caused runtime mismatches, leading to crashes when destroying C++ standard library objects.

This was observed with local std::stringstream instances, but likely affects other STL types relying on shared runtime state (e.g. std::locale, iostreams, allocators).

Switched to dynamic linking of libstdc++ to ensure compatibility with Unity’s runtime environment.