Make it have the semantics of subtype.

This fixes building `bootstrap` using a local Rust nightly.

Instead of checking every element, we can check the whole memory
range at once.

This allows it to print out the "late-bound regions" from the closure
context more easily. Besides, all the state that is being printed it
is private to the `UniversalRegions`.

This reverts (part of) commit cb9a336ae2cf6a75fdcc130853286349cb424c96.

Also, adjust the MAX to be `u32::MAX - 1`, leaving room for `u32::MAX`
to become a sentinel value in the future.

Signed-off-by: NMarc-Antoine Perennou <Marc-Antoine@Perennou.com>

We're shipping a rust-enabled lldb, but the "lldb" executable is not
installed into the "bin" directory by rustup.  See the discussion in
https://github.com/rust-lang-nursery/rustup.rs/pull/1492 for
background on this decision.  There, we agreed to have rust-lldb
prefer the rust-enabled lldb if it is installed.

This patch changes dist.rs to put lldb into rustlib, following what
was done for the other LLVM tools in #53955, and then fixes rust-lldb
to prefer that lldb, if it exists.

See issue #48168