Changes

[WinASan] Improve exception reporting accuracy

Previously, ASan would produce reports like this:
ERROR: AddressSanitizer: breakpoint on unknown address 0x000000000000 (pc 0x7fffdd7c5e86 ...)

This is unhelpful, because the developer may think this is a null
pointer dereference, and not a breakpoint exception on some PC.

The cause was that SignalContext::GetAddress would read the
ExceptionInformation array to retreive an address for any kind of
exception. That data is only available for access violation exceptions.
This changes it to be conditional on the exception type, and to use the
PC otherwise.

I added a variety of tests for common exception types:
- int div zero
- breakpoint
- ud2a / illegal instruction
- SSE misalignment

I also tightened up IsMemoryAccess and GetWriteFlag to check the
ExceptionCode rather than looking at ExceptionInformation[1] directly.

Differential Revision: https://reviews.llvm.org/D92344

clang/test: Remove platform-linker feature

By explicitly requesting the system linker with `-fuse-ld=`, the
tests are able to CHECK for the system linker even with
CLANG_DEFAULT_LINKER=lld.

Alternative to D74704.

Differential Revision: https://reviews.llvm.org/D92291

[mlir] Small cleanups to func-bufferize/finalizing-bufferize

- Address TODO in scf-bufferize: the argument materialization issue is
  now fixed and the code is now in Transforms/Bufferize.cpp
- Tighten up finalizing-bufferize to avoid creating invalid IR when
  operand types potentially change
- Tidy up the testing of func-bufferize, and move appropriate tests
  to a new finalizing-bufferize.mlir
- The new stricter checking in finalizing-bufferize revealed that we
  needed a DimOp conversion pattern (found when integrating into npcomp).
  Previously, the converion infrastructure was blindly changing the
  operand type during finalization, which happened to work due to
  DimOp's tensor/memref polymorphism, but is generally not encouraged
  (the new pattern is the way to tell the conversion infrastructure that
  it is legal to change that type).

Lex: Update Module::findHeader to return FileEntryRef, NFC

Update `Module::findHeader` to return `Optional<FileEntryRef>` and
fix its one caller.

Differential Revision: https://reviews.llvm.org/D90485

Don't count attributes when addressing operands.

Fixes out-of-bound access in generated nested DAG rewriter matching code.

Reviewed By: tpopp

Differential Revision: https://reviews.llvm.org/D92075

[llvm] Fix for failing test from cf8ff75bade763b054476321dcb82dcb2e7744c7

Handle null values when handling operand changes for DSOLocalEquivalent.

Recommit "[llvm-symbolizer] Switch to using native symbolizer by default on Windows"

This reverts commit 1b63177a56e8cd6196778d2b90295f03e96b5800.

[clang][Fuchsia] Add relative-vtables multilib

This adds a multilib for Fuchsia that is built with the relative vtables
ABI.

Revert "[clang][Fuchsia] Add relative-vtables multilib"

This reverts commit 7c2bc3b71dc072987d43a2a86609871bd01f981f.

Forgot to add the ifferential revision.

[clang][Fuchsia] Add relative-vtables multilib

This adds multilibs for Fuchsia that is built with the relative vtables ABI,
one with and another without exceptions.

Differential Revision: https://reviews.llvm.org/D85576

[GlobalISel] Fix -Wunused-variable

[GlobalISel] Fix -Wunused-variable in -DLLVM_ENABLE_ASSERTIONS=off builds

Revert "[clang][Fuchsia] Add relative-vtables multilib"

This reverts commit fdbd84c6c819d4462546961f6086c1524d5d5ae8.

Reverting due to failing CI builders for Fuchsia's toolchain:
https://luci-milo.appspot.com/p/fuchsia/builders/ci/clang-linux-x64/b8862150211240186992?

Add help text for -nogpuinc

Differential Revision: https://reviews.llvm.org/D92339

[lldb] Refactor GetDeviceSupportDirectoryNames and GetPlatformName (NFC)

Both functions are effectively returning a single string literal. Change
the interface to return a llvm::StringRef instead of populating a vector
of std::strings or returning a std::string respectively.