> libdl exists only in MinGW64, I think.

> Why do you need it? is it because the code uses dlopen/dlsym
> somewhere?

The code uses `dynlib_open` and `dynlib_sym` which are implemented using libdl
in Posix systems. The original libgccjit uses it to implement the
`compile_to_memory` function that we do not use. The version of libgccjit I am
using implements that feature using native Windows functions, so libdl is not
necessary.

I don't think we can remove it because that part of the code runs only when the
platform is not Mingw, and in that case libdl is necessary.

> I think it's good to #undef each symbol before defining it.

Fixed in the new patch.