This commit goes through and updates various `#[cfg]` as appropriate to
get the wasm64-unknown-unknown target behaving similarly to the
wasm32-unknown-unknown target. Most of this is just updating various
conditions for `target_arch = "wasm32"` to also account for `target_arch
= "wasm64"` where appropriate. This commit also lists `wasm64` as an
allow-listed architecture to not have the `restricted_std` feature
enabled, enabling experimentation with `-Z build-std` externally.

The main goal of this commit is to enable playing around with
`wasm64-unknown-unknown` externally via `-Z build-std` in a way that's
similar to the `wasm32-unknown-unknown` target. These targets are
effectively the same and only differ in their pointer size, but wasm64
is much newer and has much less ecosystem/library support so it'll still
take time to get wasm64 fully-fledged.

These are all stable as-of-now in the WebAssembly specification so any
engine which implements wasm64 will surely implement these features as
well.

This commit works around a crash in LLVM when the
`-generate-arange-section` argument is passed to LLVM. An LLVM bug is
opened for this and the code in question is also set to continue passing
this flag with LLVM 14, assuming that this is fixed by the time LLVM 14
comes out. Otherwise this should work around debuginfo crashes on LLVM
13.

* Add wasm64 variants for inline assembly along the same lines as wasm32
* Update a few directives in libtest to check for `target_family`
  instead of `target_arch`
* Update some rustc codegen and typechecks specialized for wasm32 to
  also work for wasm64.

Brings in some fixes and better support for the wasm64 target.

This pulls in a fix for wasm64 to work correctly with this dlmalloc

Ensure that they compile with the now-a-feature-is-required logic.

Co-authored-by: Josh Triplett <josh@joshtriplett.org>

This follows from discussion on
https://bugs.llvm.org/show_bug.cgi?id=52442 where it looks like this
section doesn't make sense for wasm targets.