Ok, so, apparently the issue is with a ton of exposed symbols. Building with cmake seems to be fine. If you want to build with Projucer instead, you need to add these flags:
-fvisibility=hidden
-fvisibility-inlines-hidden
-Wl,--no-undefined
I really think Projucer should add these flags by default…
Thanks @robbert-vdh for the help! I can now finally sleep 