Previously, device info was returned as a queue with each element having
a "Level" field indicating its nesting level. This replaces this queue
with a more traditional tree-like structure.

This should not result in a change to the output of
`llvm-offload-device-info`.

[Offload] Use new error code handling mechanism

This removes the old ErrorCode-less error method and requires
every user to provide a concrete error code. All calls have been
updated.

In addition, for consistency with error messages elsewhere in LLVM, all
messages have been made to start lower case.

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

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).

We already used a flat array of kernel launch parameters for the AMD GPU
launch but now we also use this scheme for the NVIDIA GPU launch. The
only remaining/required use of the indirection is the host plugin (due
ot ffi). This allows to us simplify the use for non-OpenMP kernel
launch.

Summary:
Currently, we register images into a linear table according to the
logical OpenMP device identifier. We then initialize all of these images
as one block. This logic requires that images are compatible with *all*
devices instead of just the one that it can run on. This prevents us
from running on systems with heterogeneous devices (i.e. image 1 runs on
device 0 image 0 runs on device 1).

This patch reworks the logic by instead making the compatibility check a
per-device query. We then scan every device to see if it's compatible
and do it as they come.

Use llvm::Triple:aarch64 as the little-endian triple.

Fixes commit 3e54768d7a0e1cfa65e892b6602993192ecad91e.

This patch overhauls the `libomptarget` and plugin interface. Currently,
we define a C API and compile each plugin as a separate shared library.
Then, `libomptarget` loads these API functions and forwards its internal
calls to them. This was originally designed to allow multiple
implementations of a library to be live. However, since then no one has
used this functionality and it prevents us from using much nicer
interfaces. If the old behavior is desired it should instead be
implemented as a separate plugin.

This patch replaces the `PluginAdaptorTy` interface with the
`GenericPluginTy` that is used by the plugins. Each plugin exports a
`createPlugin_<name>` function that is used to get the specific
implementation. This code is now shared with `libomptarget`.

There are some notable improvements to this.
1. Massively improved lifetimes of life runtime objects
2. The plugins can use a C++ interface
3. Global state does not need to be duplicated for each plugin +
   libomptarget
4. Easier to use and add features and improve error handling
5. Less function call overhead / Improved LTO performance.

Additional changes in this plugin are related to contending with the
fact that state is now shared. Initialization and deinitialization is
now handled correctly and in phase with the underlying runtime, allowing
us to actually know when something is getting deallocated.

Depends on https://github.com/llvm/llvm-project/pull/86971
https://github.com/llvm/llvm-project/pull/86875
https://github.com/llvm/llvm-project/pull/86868