remove allows_weak_linkage target spec flag The flag doesn't actually do anything. I have no idea what it's original purpose was. It got introduced in https://github.com/rust-lang/rust/commit/59cfe904dcfbe2c3ad5396131b3d3ba6b7179fdd, but already a few months later in https://github.com/rust-lang/rust/commit/57950982b27c6ab45509c1f2db4a01fa1d2cfebb both of its uses were removed when the entire file `src/librustc_trans/closure.rs` got deleted. It seems like back in the day we used weak linkage for closures by default and MinGW wasn't happy about that? But not much later the way we compile closures got changed, making the work-around unnecessary. The flag has then persisted unused for 10 years. A couple of Windows/UEFI targets are setting `allows_weak_linkage: false` but I assume that was just cargo-culted. But to be sure, let's ping the folks listed for the affected targets and other Windows folks: @dvdhrm @nicholasbishop @Berrysoft @mati865 @thomcc @tbu- @ChrisDenton