Summary:
This was originally kept separate so it didn't pollute the name space,
but now I'm thinking it's just easier to bundle it in with the default
interface. This means that we'll have a bit of extra code for people
using the server.h file to handle libc opcodes, but it's minimal (3
functions) and it simplifies this.

I'm doing this because I'm hoping to move the GPU tester binary to
liboffload which handles `libc` opcodes internally except these. This is
the easier option compared to adding a hook to register custom handlers
there.

Summary:
RPC_ is a generic prefix here, use LIBC_ to indicate that these are
opcodes used to implement the C library

Summary:
The AMDGPU backend can handle wavefront sizes of 32 and 64, with the
native hardware preferring one or the other. The user can override the
hardware with `-mwavefrontsize64` or `-mwavefrontsize32` which
previously wasn't handled. We need to know the wavefront size to know
how much memory to allocate and how to index the RPC buffer. There isn't
a good way to do this with ROCm so we just use the LLVM support for
offloading to check this from the image.

Summary:
Previous patches have made the `rpc.h` header independent of the `libc`
internals. This allows us to include it directly rather than providing
an indirect C API. This patch only does the work to move the header. A
future patch will pull out the `rpc_server` interface and simply replace
it with a single function that handles the opcodes.

With some header fix forward for GPU builds.

Summary:
Recent changes added an include path in the float128 type that used the
internal `libc` path to find the macro. This doesn't work once it's
installed because we need to search from the root of the install dir.
This patch adds "include/" to the include path so that our inclusion
of installed headers always match the internal use.

Summary:
We call the global constructors by function pointer. For whatever reason
the NVPTX architecture relies very specifically on the arguments to the
function pointer invocation matching what the function is implemented
as. This is problematic as most of these constructors are generated
with no arguments. This patch removes the extended arguments that GNU
and LLVM use for the constructors optionally so that it can support the
common case.