Meson breakage
BSD breakage: Unless explicitly passing "-Wno-typedef-redefinition" and "-Wno-missing-field-initializers", builds would fail not only on macOS, but also on BSDs.Knowing that, let's just use disable those warnings when not building on Linux.
mingw breakage:
Let's disable gtk-doc build when performing a cross-build as
./Libosinfo-scan
will be generated for the cross architecture and
cannot be run from the host machine architecture.