The GPU stdio functions were depending on indirect inclusion for some of
their dependencies. This patch should fix all of that.

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

Summary:
I'm going to attempt to move the `rpc.h` header to a separate folder
that we can install and include outside of `libc`. Before doing this I'm
going to try to trim up the file so there's not as many things I need to
copy to make it work. This dependency on `cpp::functional` is a low
hanging fruit. I only did it so that I could overload the argument of
the work function so that passing the id was optional in the lambda,
that's not a *huge* deal and it makes it more explicit I suppose.

This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.

reland of https://github.com/llvm/llvm-project/pull/98215

Additionally adds proxy headers for FILE and the fopencookie types

The arm32 build has been failing due to redefinitions of the off_t type.
This patch fixes this by moving off_t to a proper proxy header. To do
this, it also moves stdio macros to a proxy header to hopefully avoid
including this proxy header alongside this public stdio.h.

This is step 4 of
https://discourse.llvm.org/t/rfc-customizable-namespace-to-allow-testing-the-libc-when-the-system-libc-is-also-llvms-libc/73079

Summary:
This patch implements the `fgets`, `getc`, `fgetc`, and `getchar`
functions on the GPU. Their implementations are straightforward enough.
One thing worth noting is that the implementation of `fgets` will be
extremely slow due to the high latency to read a single char. A faster
solution would be to make a new RPC call to call `fgets` (due to the
special rule that newline or null breaks the stream). But this is left
out because performance isn't the primary concern here.