The source project of this merge request has been removed.
main/lua5.4: add c++ pkgconfig
debian seems to have it https://salsa.debian.org/lua-team/lua5.4/-/blob/master/debian/lua-c++.pc.in
and it seems to actually be used by some people (see !34167 (merged)).
also add the extern C guard to make lua safe to import from C++