This flag was used to let us incrementally introduce debug records
into LLVM, however everything is now using records. It serves no
purpose now, so delete it.

Avoid using report_fatal_error. Many more uses that should be converted
in the pass remain.

This fixes #139614 on non-clang compilers by moving `__has_warning`
completely inside the `#if defined(__clang__)` block. This prevents a
parse failure from compilers which don't recognize `__has_warning`.

Original description:
Followup to #138741.

This adds the requested macro to silence
`-Wunnecessary-virtual-specifier` when declaring virtual anchor
functions in `final` classes, per [LLVM
policy](https://llvm.org/docs/CodingStandards.html#provide-a-virtual-method-anchor-for-classes-in-headers).

It also cleans up any remaining instances of the warning, allowing us to
stop disabling it when we build LLVM.

These are identified by misc-include-cleaner.  I've filtered out those
that break builds.  Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.

This reverts commit 0954c9d487e7cb30673df9f0ac125f71320d2936.

It breaks the build when built with gcc version 11.4.0 (Ubuntu 11.4.0-1ubuntu1~22.04).

Followup to #138741.

This adds the requested macro to silence
`-Wunnecessary-virtual-specifier` when declaring virtual anchor
functions in `final` classes, per [LLVM
policy](https://llvm.org/docs/CodingStandards.html#provide-a-virtual-method-anchor-for-classes-in-headers).

It also cleans up any remaining instances of the warning, allowing us to
stop disabling it when we build LLVM.

Some application code operating on generic pointers (that then gete
initialized to buffer fat pointers) may perform tests against nullptr.
After address space inference, this results in comparisons against
`addrspacecast (ptr null to ptr addrspace(7))`, which were crashing.

However, while general casts to ptr addrspace(7) from generic pointers
aren't supposted, it is possible to cast null pointers to the all-zerose
bufer resource and 0 offset, which this patch adds.

It also adds a TODO for casting _out_ of buffer resources, which isn't
implemented here but could be.

This PR adds a amdgns_load_to_lds intrinsic that abstracts over loads to
LDS from global (address space 1) pointers and buffer fat pointers
(address space 7), since they use the same API and "gather from a
pointer to LDS" is something of an abstract operation.

This commit adds the intrinsic and its lowerings for addrspaces 1 and 7,
and updates the MLIR wrappers to use it (loosening up the restrictions
on loads to LDS along the way to match the ground truth from target
features).

It also plumbs the intrinsic through to clang.

This patch adds support for LLVM IR atomicrmw `fmaximum` and `fminimum`
instructions.

These mirror the `llvm.maximum.*` and `llvm.minimum.*` instructions, but
are atomic and use IEEE754 2019 handling for NaNs, which is different to
`fmax` and `fmin`. See:
     https://llvm.org/docs/LangRef.html#llvm-minimum-intrinsic
for more details.

Future changes will allow this LLVM IR to be lowered to specialised
assembler instructions on suitable targets, such as AArch64.