This is just a stub for now.

[AMDGPU][NFC] Replace gfx940 and gfx941 with gfx942 in llvm/test

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

This PR uses gfx942 instead of gfx940 and gfx941 in the test RUN-lines (unless there is already a RUN-line for gfx942).

The only notable difference in the test output is that gfx942 does not force the use of sc0 and sc1 on stores while gfx940 and gfx941 do (cf. https://reviews.llvm.org/D149986).

For SWDEV-512631

Mostly a stub, but adds some baseline tests and
tests for removed instructions.

This patch introduces a new generic target, `gfx9-4-generic`. Since it doesn’t support FP8 and XF32-related instructions, the patch includes several code reorganizations to accommodate these changes.

These generic targets include multiple GPUs and will, in the future,
provide a way to build once and run on multiple GPU, at the cost of less
optimization opportunities.

Note that this is just doing the compiler side of things, device libs an
runtimes/loader/etc. don't know about these targets yet, so none of them
actually work in practice right now. This is just the initial commit to
make LLVM aware of them.

This contains the documentation changes for both this change and #76954
as well.

Define target names and ELF numbers for new GFX12 targets gfx1200 and
gfx1201. For now they behave identically to GFX11.

The issue is uncovered by #47698: for assembly files, -triple= specifies the
full target triple while -arch= merely sets the architecture part of the default
target triple, leaving a target triple which may not make sense, e.g.
riscv64-apple-darwin.

Therefore, -arch= is error-prone and not recommended for tests. The issue has
been benign as we recognize $unknown-apple-darwin as ELF instead of rejecting it
outrightly.

Due to the nature of the issue, we don't see the issue in tests using
architectures that any of Mach-O/COFF/XCOFF supports.