meson: Don't link against libpython on non-Windows systems. Fixes #253

Christoph Reiter requested to merge meson-dont-link-libpython into master

While on Windows it needs to link against it, on Unix systems it doesn't have to if the process loading it has all the symbols already loaded (python executable itself, or something dlopening libpython with RTLD_GLOBAL before).

While on Fedora things get linked by default that's not the case with Debian based distros and macOS, so most software has to deal with it anyway and we ignore Fedora here for now.

Ideally this should get handled in meson itself, see:

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