Allow `global_asm!` in statement positions
This PR makes it possible to put `global_asm!` in statement positions. This is particularly useful for proc-macros, where you otherwise have to wrap them in `mod foo { global_asm!(...); }`.
I'm happy to open an ACP first (or a design meeting?).
I would also assume this needs sign-off from the lang-team?
Previously discussed on [Zulip](https://rust-lang.zulipchat.com/#narrow/channel/216763-project-inline-asm/topic/Item.20position.20global_asm/with/581784943).
r? @Amanieu
Jonathan Brouwer
59eda84e03