We introduced VariantKinds after MCSymbolRefExpr::VariantKind and then
deprecated the VariantKind naming in favor of AtSpecifier (#133214).
Rename the function and type to use the recommended convention.

Introduce MCAsmInfo::UsesSetToEquateSymbol to control the preferred
syntax for symbol equating. We now favor the more readable and common
`symbol = expression` syntax over `.set`. This aligns with pre- https://reviews.llvm.org/D44256 behavior.

On Apple platforms, this resolves a clang -S vs -c behavior difference (resolves #104623).

For targets whose = support is unconfirmed, UsesSetToEquateSymbol is set to false.
This also minimizes test updates.

Pull Request: https://github.com/llvm/llvm-project/pull/142289

Similar to previous migration done for all other ELF targets.
Switch from the confusing `VariantKind` to `Specifier`, which aligns
with Arm and IBM AIX's documentation.

Moving forward, relocation specifiers should be integrated into
AMDGPUMCExpr rather than MCSymbolRefExpr::SubclassData.

(Note: the term AMDGPUMCExpr::VariantKind is for expressions
without relocation specifiers:
https://github.com/llvm/llvm-project/pull/82022

It's up to AMDGPU maintainers to integrate these constants into Specifier.
)

Pull Request: https://github.com/llvm/llvm-project/pull/133608

Follow-up to 14951a5a3120e50084b3c5fb217e2d47992a24d1

* Unify getVariantKindName and getVariantKindForName
* Allow each target to specify the preferred case (albeit ignored in MCParser)

Note: targets that use variant kinds should call MCExpr::print with a
non-null MAI to print variant kinds. operator<< passes a nullptr to
`MCExpr::print`, which should be avoided (e.g. Hexagon; fixed in
commit cf00ac81ac049cddb80aec1d6d88b8fab4f209e8).

These use a new VOP3PX encoding for the v_mfma_scale_* instructions,
which bundles the pre-scale v_mfma_ld_scale_b32. None of the modifiers
are supported yet (op_sel, neg or clamp).

I'm not sure the intrinsic should really expose op_sel (or any of the
others). If I'm reading the documentation correctly, we should be able
to just have the raw scale operands and auto-match op_sel to byte
extract patterns.

The op_sel syntax also seems extra horrible in this usage, especially with the
usual assumed op_sel_hi=-1 behavior.

The variable and its comment could lead to confusion (AMDGPU
unnecessarily set it).

For some reasons `SunStyleELFSectionSwitchSyntax` is set to `true` for
AMDGPU, but according to
https://github.com/llvm/llvm-project/issues/64862#issuecomment-1880419239
that syntax is only limited to Sun system.

Fix #64862.

Consider only targets where `MCAsmInfo::ExceptionsType == ExceptionHandling::None`
and that support CFI (when `MCAsmInfo::UsesCFIForDebug` is set to true):
currently, only AMDGPU.

This patch enables the emission of CFI information in the .eh_frame
section when the uwtable attribute is present on a function.

Before, we could generate CFI information for debugging puproses only.

This patch prepares AMDGPU to support collecting GPU stack traces in the future.

I did a first implementation (https://reviews.llvm.org/D139024)
but at the time I had not realized that no other platform used
`UsesCFIForDebug`.

Reviewed By: scott.linder

Differential Revision: https://reviews.llvm.org/D151806