libsyntax: remove dead code find_linkage_metas

Closes #14329
librustc: Make addresses of immutable statics insignificant unless
`#[inline(never)]` is used.

Closes #8958.

This can break some code that relied on the addresses of statics
being distinct; add `#[inline(never)]` to the affected statics.

[breaking-change]
auto merge of #14977 : pcwalton/rust/address-insignificant-reform, r=brson

`#[inline(never)]` is used.

Closes #8958.

This can break some code that relied on the addresses of statics
being distinct; add `#[inline(never)]` to the affected statics.

[breaking-change]

r? @brson
Remove TraitStore from ty_trait

Use ty_rptr/ty_uniq(ty_trait) rather than TraitStore to represent trait types.
Also addresses (but doesn't close) #12470.
Part of the work towards DST (#12938).

[breaking-change] lifetime parameters in `&mut trait` are now invariant. They used to be contravariant.
auto merge of #14956 : nathantypanski/rust/master, r=alexcrichton

Closes #14329

Recent-ish uses of `find_linkage_metas` from my `git grep` output are [here](https://gist.github.com/nathantypanski/b9d2d453718a22765f5c), for those interested who wish to tread through the history.
auto merge of #14869 : nick29581/rust/tstore, r=nmatsakis

Use ty_rptr/ty_uniq(ty_trait) rather than TraitStore to represent trait types.
Also addresses (but doesn't close) #12470.
Part of the work towards DST (#12938).