[libc] Make the RPC server target always available

[jhuber6]

Summary

This patch makes sure that we always build the RPC server. The proposed
used for this is to begin integrating this server implementation into
libomptarget. That requires that we build this server ahead of time
when using a LLVM_ENABLE_PROJECTS build. Make a few tweaks to ensure
that the GCC compiler which may be used for this build doesn't complain.

[JonChesterfield]

libc/utils/gpu/server/CMakeLists.txt

10

This may grow complexity over time :(

libc/CMakeLists.txt

 endif()
 
 option(LIBC_HDRGEN_ONLY "Only build the 'libc-hdrgen' executable" OFF)
 if(("libc" IN_LIST LLVM_ENABLE_RUNTIMES AND NOT LLVM_RUNTIMES_BUILD) OR 
    LIBC_HDRGEN_ONLY)
   # When libc is build as part of the runtimes/bootstrap build's CMake run, we
   # only need to build the host tools to build the libc. So, we just do enough
   # to build libc-hdrgen and return.
+
+  # Always make the RPC server availible to other projects for GPU mode.
+  if(LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES)
+    add_subdirectory(utils/gpu/server)
+  endif()
   return()
 endif()
 
 option(LIBC_CMAKE_VERBOSE_LOGGING
        "Log details warnings and notifications during CMake configuration." OFF)
 # Path libc/scripts directory.
 set(LIBC_BUILD_SCRIPTS_DIR "${LIBC_SOURCE_DIR}/utils/build_scripts")
 

libc/utils/gpu/server/CMakeLists.txt

 add_library(llvmlibc_rpc_server STATIC rpc_server.cpp)
 
 # Include the RPC implemenation from libc.
 target_include_directories(llvmlibc_rpc_server PRIVATE ${LIBC_SOURCE_DIR})
 target_include_directories(llvmlibc_rpc_server PUBLIC ${LIBC_SOURCE_DIR}/include)
 target_include_directories(llvmlibc_rpc_server PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
 
+# Ignore unsupported clang attributes if we're using GCC.
+target_compile_options(llvmlibc_rpc_server PUBLIC
+                       $<$<CXX_COMPILER_ID:GNU>:-Wno-attributes>)
+
 # Install the server and associated header.
 install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/rpc_server.h
         DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/gpu-none-llvm/
         COMPONENT libc)
 install(TARGETS llvmlibc_rpc_server
         ARCHIVE DESTINATION "lib${LLVM_LIBDIR_SUFFIX}"
         COMPONENT libc)

libc/utils/gpu/server/rpc_server.h

 extern "C" {
 #endif
 
 /// The maxium number of ports that can be opened for any server.
 const uint64_t RPC_MAXIMUM_PORT_COUNT = 64;
 
 /// The symbol name associated with the client for use with the LLVM C library
 /// implementation.
-static const char *rpc_client_symbol_name = "__llvm_libc_rpc_client";
+inline const char *rpc_client_symbol_name = "__llvm_libc_rpc_client";
 
 /// status codes.
 typedef enum {
   RPC_STATUS_SUCCESS = 0x0,
   RPC_STATUS_CONTINUE = 0x1,
   RPC_STATUS_ERROR = 0x1000,
   RPC_STATUS_OUT_OF_RANGE = 0x1001,
   RPC_STATUS_UNHANDLED_OPCODE = 0x1002,