[wip/meson] -Wimplicit-fallthrough is not supported by clang
No problem with gcc. But with clang, these errors appear during 'gobject-introspection' compilation :
error: unannotated fall-through between switch labels [-Werror,-Wimplicit-fallthrough]
Because most of these errors come during flex generation (so not a vala related error), I don't recommend clang for compiling.