[libc] Move RPC interface to `libc/shared` to export it (#117034)

Summary:
Previous patches have made the `rpc.h` header independent of the `libc`
internals. This allows us to include it directly ra

[libc] Move RPC interface to `libc/shared` to export it (#117034)

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.

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[libc] Revert https://github.com/llvm/llvm-project/pull/83199 since it broke Fuchsia. (#83374)

With some header fix forward for GPU builds.

[libc] Add "include/" to the LLVM include directories (#83199)

Summary:
Recent changes added an include path in the float128 type that used the
internal `libc` path to find the macro. This doesn't w

[libc] Add "include/" to the LLVM include directories (#83199)

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.

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[libc] Mass replace enclosing namespace (#67032)

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

[libc] Remove test RPC opcodes from the exported header

This patch does the noisy work of removing the test opcodes from the
exported interface to an interface that is only visible in `libc`. The
be

[libc] Remove test RPC opcodes from the exported header

This patch does the noisy work of removing the test opcodes from the
exported interface to an interface that is only visible in `libc`. The
benefit of this is that we both test the exported RPC registration more
directly, and we do not need to give this interface to users.

I have decided to export any opcode that is not a "core" libc feature as
having its MSB set in the opcode. We can think of these as non-libc
"extensions".

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D154848

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[libc][NFC] Rename files

This patch mostly renames files so it better reflects the function they declare.

Reviewed By: michaelrj

Differential Revision: https://reviews.llvm.org/D155607

[libc] Export GPU extensions to `libc` for external use

The GPU port of the LLVM C library needs to export a few extensions to
the interface such that users can interface with it. This patch adds th

[libc] Export GPU extensions to `libc` for external use

The GPU port of the LLVM C library needs to export a few extensions to
the interface such that users can interface with it. This patch adds the
necessary logic to define a GPU extension. Currently, this only exports
a `rpc_reset_client` function. This allows us to use the server in
D147054 to set up the RPC interface outside of `libc`.

Depends on https://reviews.llvm.org/D147054

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D152283

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[libc] Fix the `send_n` and `recv_n` utilities under divergent lanes

We provide the `send_n` and `recv_n` utilities as a generic way to
stream data between both sides of the process. This was previo

[libc] Fix the `send_n` and `recv_n` utilities under divergent lanes

We provide the `send_n` and `recv_n` utilities as a generic way to
stream data between both sides of the process. This was previously
tested and performed as expected when using a string of constant size.
However, when the size was allowed to diverge between the threads in the
warp or wavefront this could deadlock. This did not occur on NVPTX
because of the use of the explicit warp sync. However, on AMD one of the
work items in the wavefront could continue executing and hit the next
`recv` call before the other threads, then we would deadlock as we
violated the RPC invariants.

This patch replaces the for loop with a thread ballot. This will cause
every thread in the warp or wavefront to continue executing the loop
until all of them can exit. This acts as a more explicit wavefront sync.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D150992

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[libc] Fix undeclared 'free' function in stream test

Summary:
We need this function from the test.cpp but need to declare it manually.

[libc] Implement a generic streaming interface in the RPC

Currently we provide the `send_n` and `recv_n` functions. These were
somewhat divergent and not tested on the GPU. This patch changes the
su

[libc] Implement a generic streaming interface in the RPC

Currently we provide the `send_n` and `recv_n` functions. These were
somewhat divergent and not tested on the GPU. This patch changes the
support to be more common. We do this my making the CPU provide an array
equal the to at least the lane size while the GPU can rely on the
private memory address of its stack variables. This allows us to send
data back and forth generically.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D150379

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