Fixes #45638

These were already broken for debug builds.

In #46382 the logic around linkage preservation with ThinLTO ws tweaked but the
loop that registered all otherwise exported GUID values as "don't internalize
me please" was erroneously too conservative and only asking "external" linkage
items to not be internalized. Instead we actually want the inversion of that
condition, everything *without* "local" linkage to be internalized.

This commit updates the condition there, adds a test, and...

Closes #46543

suggested by arielb1

as suggested by arielb1

This includes the additional case suggested by arielb1.

It's just not useful. It also makes it hard to have tests that probe
internal state, since the interning number is very sensitive.

Dumping the number in the case of gensym is not ideal but will do for
now.

The overall format is now easier to read. Also, There is now graphviz
output, as well as a `#[rustc_regions]` annotation that dumps internal
state.

We also rename some of the files to conform to the
feature-gate-<feat_name>.rs pattern that is most common.

Renames only in this commit, and obviously
.stderr file additions.

Fixes #46519.

Patch as suggested by eddyb:
https://github.com/rust-lang/rust/issues/46519#issuecomment-349443519

This fixes the tests for issue #29793