flexlink: simplify static linking with libstdc++

[kit-ty-kate]

Currently with flexlink, if you have a C++ binding and want to link it statically in your executable to avoid having to carry the dll around the only option that works is to manually set the name for the archive file like this (with MinGW):

-l:libstdc++.a -l:libpthread.a -Wl,-static

It would be nice if something like -lstdc++ -static was a thing so that flexlink can find the correct archive file as by default -lstdc++ -Wl,-static will use libstdc++.dll.a which is the shared version of libstdc++ and not the static one.