Generate nuw GEPs for struct member accesses, as inbounds + non-negative
implies nuw.

Regression tests are updated using update scripts where possible, and by
find + replace where not.

This is a follow-up from the conversation starting at
https://github.com/llvm/llvm-project/pull/93809#issuecomment-2173729801

The root problem that motivated the change are external AST sources that
compute `ASTRecordLayout`s themselves instead of letting Clang compute
them from the AST. One such example is LLDB using DWARF to get the
definitive offsets and sizes of C++ structures. Such layouts should be
considered correct (modulo buggy DWARF), but various assertions and
lowering logic around the `CGRecordLayoutBuilder` relies on the AST
having `[[no_unique_address]]` attached to them. This is a
layout-altering attribute which is not encoded in DWARF. This causes us
LLDB to trip over the various LLVM<->Clang layout consistency checks.
There has been precedent for avoiding such layout-altering attributes
from affecting lowering with externally-provided layouts (e.g., packed
structs).

This patch proposes to replace the `isZeroSize` checks in
`CGRecordLayoutBuilder` (which roughly means "empty field with
[[no_unique_address]]") with checks for
`CodeGen::isEmptyField`/`CodeGen::isEmptyRecord`.

**Details**
The main strategy here was to change the `isZeroSize` check in
`CGRecordLowering::accumulateFields` and
`CGRecordLowering::accumulateBases` to use the `isEmptyXXX` APIs
instead, preventing empty fields from being added to the `Members` and
`Bases` structures. The rest of the changes fall out from here, to
prevent lookups into these structures (for field numbers or base
indices) from failing.

Added `isEmptyRecordForLayout` and `isEmptyFieldForLayout` (open to
better naming suggestions). The main difference to the existing
`isEmptyRecord`/`isEmptyField` APIs, is that the `isEmptyXXXForLayout`
counterparts don't have special treatment for `unnamed bitfields`/arrays
and also treat fields of empty types as if they had
`[[no_unique_address]]` (i.e., just like the `AsIfNoUniqueAddr` in
`isEmptyField` does).

Just re-running the script to make future updates easier

Avoid diffs from no longer hardcoding metadata checks

The script changes over time and unrelated changes to the test check
lines should not pollute future revisions.

Conversion performed using the script at:
https://gist.github.com/nikic/98357b71fd67756b0f064c9517b62a34

These are only tests where no manual fixup was required.

I used a script to reuse existing check lines rather than creating new
ones. There are more opportunities to reduce the line count but the
"check generated functions" logic makes that somewhat tricky.

FWIW, we really should redo the update script with all these use cases
in mind...

Differential Revision: https://reviews.llvm.org/D128686

This adds -no-opaque-pointers to clang tests whose output will
change when opaque pointers are enabled by default. This is
intended to be part of the migration approach described in
https://discourse.llvm.org/t/enabling-opaque-pointers-by-default/61322/9.

The patch has been produced by replacing %clang_cc1 with
%clang_cc1 -no-opaque-pointers for tests that fail with opaque
pointers enabled. Worth noting that this doesn't cover all tests,
there's a remaining ~40 tests not using %clang_cc1 that will need
a followup change.

Differential Revision: https://reviews.llvm.org/D123115

When adding new attributes, existing attributes are dropped. While
this appears to be a longstanding issue, this was highlighted by D105169
which dropped a lot of attributes due to adding the new noundef
attribute.

Ahmed Bougacha (@ab) tracked down the issue and provided the fix in
CGCall.cpp. I bundled it up and updated the tests.

Turning on `enable_noundef_analysis` flag allows better codegen by removing freeze instructions.
I modified clang by renaming `enable_noundef_analysis` flag to `disable-noundef-analysis` and turning it off by default.

Test updates are made as a separate patch: D108453

Reviewed By: eugenis

Differential Revision: https://reviews.llvm.org/D105169