No tests yet, but it will allow further tests not to be
polluted with these waits.

This annotates the `Twine` passed to the constructors of the various
DiagnosticInfo subclasses with `[[clang::lifetimebound]]`, which causes
us to warn when we would try to print the twine after it had already
been destructed.

We also update `DiagnosticInfoUnsupported` to hold a `const Twine &`
like all of the other DiagnosticInfo classes, since this warning allows
us to clean up all of the places where it was being used incorrectly.

This was only used for gfx940 and gfx941, which have since been removed.

For SWDEV-512631

gfx940 and gfx941 are no longer supported. This is one of a series of
PRs to remove them from the code base.

This PR removes all non-documentation occurrences of gfx940/gfx941 from
the llvm directory, and the remaining occurrences in clang.

Documentation changes will follow.

For SWDEV-512631

global_wb with scopes lower than SCOPE_SYS is unnecessary for
correctness.

I was initially optimistic they would be very cheap no-ops but they can
actually be quite expensive so let's avoid them.

Documents the memory model implemented as of #98591, with some
fixes/optimizations to the implementation.

- Emit GLOBAL_WB instructions
- Reflect synscope on instructions's `scope:` operand

Fixes SWDEV-468508
Fixes SWDEV-470735
Fixes SWDEV-468392
Fixes SWDEV-469622