Summary:
Currently we depend on a single LLVM include directory. This is actually
only required to define one enum, which is highly unlikely to change.
THis patch makes the `Environment.h` include directory more hermetic so
we no long depend on other libraries. In exchange, we get a simpler
dependency list for the price of hard-coding `1` somewhere. I think it's
a valid trade considering that this flag is highly unlikely to change at
this point.

@ronlieb AMD version
https://gist.github.com/jhuber6/3313e6f957be14dc79fe85e5126d2cb3

Summary:
Previously, we removed the special handling for the code object version
global. I erroneously thought that this meant we cold get rid of this
weird `-Xclang` option. However, this also emits an LLVM IR module flag,
which will then cause linking issues.

Summary:
This patch ports the runtime to use `gpuintrin.h` instead of calling the
builtins for most things. The `lanemask_gt` stuff was left for now with
a fallback.

AMD version for Ron
https://gist.github.com/jhuber6/42014d635b9a8158727640876bf47226.

Summary:
This definition is more portable since it defines the correct value for
the target. I got rid of the helper mostly because I think it's easy
enough to use now that it's a type and being explicit about what's
`undef` or `poison` is good.

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).

Summary:
Use a normal bitcast, remove from the shared utils since it's not
available in
GCC 7.4

Summary:
This is going to be deprecated in
https://github.com/llvm/llvm-project/pull/112849. This patch ports it to
use the builtin instead. This isn't a compile constant, so it could
slightly negatively affect codegen. There really should be an IR pass to
turn it into a constant if the function has known attributes.

Using the builtin is correct when we just do it for knowing the size
like we do here. Obviously guarding w32/w64 code with this check would
be broken.

We had three `utils::` namespaces, all with different "meaning" (host,
device, hsa_utils). We should, when we can, keep "include/Shared"
accessible from host and device, thus RefCountTy has been moved to a
separate header. `hsa_utils` was introduced to make `utils::` less
overloaded. And common functionality was de-duplicated, e.g.,
`utils::advance` and `utils::advanceVoidPtr` -> `utils:advancePtr`. Type
punning now checks for the size of the result to make sure it matches
the source type.

No functional change was intended.

This reverts commit 7b4865582299294455bc816358fd88a9c6e5e0be.