Summary:
This removes the use of OpenMP offloading to build the device runtime.
The main benefit here is that we no longer need to rely on offloading
semantics to build a device only runtime. Things like variants are now
no longer needed and can just be simple if-defs. In the future, I will
remove most of the special handling here and fold it into calls to the
`<gpuintrin.h>` functions instead. Additionally I will rework the
compilation to make this a separate runtime.

The current plan is to have this, but make including OpenMP and
offloading either automatically add it, or print a warning if it's
missing. This will allow us to use a normal CMake workflow and delete
all the weird 'lets pull the clang binary out of the build' business.
```
-DRUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES=offload
-DLLVM_RUNTIME_TARGETS=amdgcn-amd-amdhsa
```

After that, linking the OpenMP device runtime will be `-Xoffload-linker
-lomp`. I.e. no more fat binary business.

Only look at the most recent commit since this includes the two
dependencies
(fix to AMDGPUEmitPrintfBinding and the PointerToMember bug).

This pull request is a revised version of #76587. This pull request
fixes some build issues that were present in the previous version of
this change.

> This pull request is the first part of an ongoing effort to extends
PGO instrumentation to GPU device code. This PR makes the following
changes:
>
> - Adds blank registration functions to device RTL
> - Gives PGO globals protected visibility when targeting a supported
GPU
> - Handles any addrspace casts for PGO calls
> - Implements PGO global extraction in GPU plugins (currently only
dumps info)
>
> These changes can be tested by supplying `-fprofile-instrument=clang`
while targeting a GPU.

This reverts commit 5fd2af38e461445c583d7ffc2fe23858966eee76. It caused build issues and broke the buildbot.

This pull request is the first part of an ongoing effort to extends PGO
instrumentation to GPU device code. This PR makes the following changes:

- Adds blank registration functions to device RTL
- Gives PGO globals protected visibility when targeting a supported GPU
- Handles any addrspace casts for PGO calls
- Implements PGO global extraction in GPU plugins (currently only dumps
info)

These changes can be tested by supplying `-fprofile-instrument=clang`
while targeting a GPU.