[libc] Make RPC server handling header only (#131205)

Summary:
This patch moves the RPC server handling to be a header only utility
stored in the `shared/` directory. This is intended to be shared within
LLVM for the loaders and `offload/` handling.

Generally, this makes it easier to share code without weird
cross-project binaries being plucked out of the build system. It also
allows us to soon move the loader interface out of the `libc` project so
that we don't need to bootstrap those and can build them in LLVM.

runtimes/cmake/Modules/FindLibcCommonUtils.cmake

@@ -1,19 +0,0 @@
-#===--------------------------------------------------------------------===//
-#
-# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-# See https://llvm.org/LICENSE.txt for details.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#
-#===--------------------------------------------------------------------===//
-
-if(NOT TARGET llvm-libc-common-utilities)
-  set(libc_path ${CMAKE_CURRENT_LIST_DIR}/../../../libc)
-  if (EXISTS ${libc_path} AND IS_DIRECTORY ${libc_path})
-    add_library(llvm-libc-common-utilities INTERFACE)
-    # TODO: Reorganize the libc shared section so that it can be included without
-    # adding the root "libc" directory to the include path.
-    target_include_directories(llvm-libc-common-utilities INTERFACE ${libc_path})
-    target_compile_definitions(llvm-libc-common-utilities INTERFACE LIBC_NAMESPACE=__llvm_libc_common_utils)
-    target_compile_features(llvm-libc-common-utilities INTERFACE cxx_std_17)
-  endif()
-endif()