Summary:
Previous change made us no longer link `exit` by default which implied
the RPC server. This is a required symbol for the loader. This will be
fixed later when I port the loader to LLVMOffload. For now just work
around it to fix the bots.

Summary:
We use the infrastructure to stand up a pretend hosted environment on
the GPU. Part of that is calling exit codes and handling the callback.
Exiting from inside a GPU region is problematic as it actually relies on
a lot of GPU magic behind the scenes. This is at least *correct* now as
we use `quick_exit` on the CPU when the GPU calls `exit`. However,
calling `quick_exit` will interfere with instrumentation or benchmarking
that expects a nice teardown order. For normal execution we should do
the friendly option and let the loader utility clean everything up
manually.

Summary:
There's an extern weak symbol for this, we should just factor these into
a more common interface. Stub them temporarily to make the bots happy.
PTXAS does not handle extern weak.

Summary:
I fixed the errors here recently so I can actually use these. This
shouldn't impact much, just should hopefully make the code generated
slightly better.

Reverts llvm/llvm-project#102825

This is invalid in C++, and clang recently started warning on it as of
#101853

Summary:
This patch implements 'getenv'. I was torn on how to implement this,
since realistically we only have access to this environment pointer in
the "loader" interface. An alternative would be to use an RPC call every
time, but I think that's overkill for what this will be used for. A
better solution is just to emit a common `DataEnvironment` that contains
all of the host visible resources to initialize. Right now this is the
`env_ptr`, `clock_freq`, and `rpc_client`.

I did this by making the `app.h` interface that Linux uses more general,
could possibly move that into a separate patch, but I figured it's
easier to see with the usage.

This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.