Summary:
We try to clamp these to ones known to work, but we should probably just
optimistically accept these. I'd prefer to update the flag check, but
since NVIDIA refuses to publish their ELF format it's too much effort to
reverse engineer.

Fixes: https://github.com/llvm/llvm-project/issues/138532

Summary:
We moved from cov4 to cov5 a long time ago, and it guards simplifying
some front end code, so we should be able to move up with this.

This adds support for the loongarch64 architecture to the offload host
plugin.

Similar to #115773

To fix some test issues, I've had to add the LoongArch64 target to:

- CompilerInvocation::ParseLangArgs
- linkDevice in ClangLinuxWrapper.cpp
- OMPContext::OMPContext (to set the device_kind_cpu trait)

Reviewed By: jhuber6

Pull Request: https://github.com/llvm/llvm-project/pull/120173

Enables generic ISA, e.g., "--offload-arch=gfx11-generic" device code to
run on gfx11-generic ISA capable device.

Executable may contain one ELF that has specific target ISA and another
ELF that has compatible generic ISA.
Under that circumstance, this code should say both ELFs are compatible,
leaving the rest to PluginManager to handle.
Suggestions on how best to address that is welcome.

This reverts commit 410cbe3cf28913cca2fc61b3437306b841d08172 because some
buildbots are not ready yet.

This adds support for the riscv64 architecture to the offload host
plugin. The check to define FFI_DEFAULT_ABI is intentionally not guarded
by __riscv_xlen as the value is the same for riscv32 and riscv64
(support for OpenMP on riscv32 is still under review).

Summary:
This gets the target's corresponding ELF value from the preprocessor.
We use this to detect if a given ELF is compatible with the CPU
offloading impolementation for OpenMP. Previously we used defitions from
CMake, but this is easier for people to understand as there may be new
users of this in the future.

In a nutshell, this moves our libomptarget code to populate the offload
subproject.

With this commit, users need to enable the new LLVM/Offload subproject
as a runtime in their cmake configuration.
No further changes are expected for downstream code.

Tests and other components still depend on OpenMP and have also not been
renamed. The results below are for a build in which OpenMP and Offload
are enabled runtimes. In addition to the pure `git mv`, we needed to
adjust some CMake files. Nothing is intended to change semantics.

```
ninja check-offload
```
Works with the X86 and AMDGPU offload tests

```
ninja check-openmp
```
Still works but doesn't build offload tests anymore.

```
ls install/lib
```
Shows all expected libraries, incl.
- `libomptarget.devicertl.a`
- `libomptarget-nvptx-sm_90.bc`
- `libomptarget.rtl.amdgpu.so` -> `libomptarget.rtl.amdgpu.so.18git`
- `libomptarget.so` -> `libomptarget.so.18git`

Fixes: https://github.com/llvm/llvm-project/issues/75124

---------

Co-authored-by: Saiyedul Islam <Saiyedul.Islam@amd.com>