[build][hexagon] fix several compiler warnings (apache#11245)

cmake/modules/Hexagon.cmake

@@ -61,7 +61,7 @@ endif()
 # the path to the SDK), unless it's needed. The flag USE_HEXAGON decides
 # whether any Hexagon-related functionality is enabled. Specifically,
 # setting USE_HEXAGON=OFF, disables any form of Hexagon support.
-# 
+#
 # Note on the function of USE_HEXAGON_RPC:
 # - When building for Hexagon, this will build the Hexagon endpoint of the
 #   RPC server: the FastRPC skel library (with TVM runtime built into it),
@@ -172,6 +172,14 @@ if(USE_HEXAGON_RPC)
           -o "${TVMRT_SOURCE_DIR}/hexagon/rpc"
       MAIN_DEPENDENCY "${TVMRT_SOURCE_DIR}/hexagon/rpc/hexagon_rpc.idl"
     )
+
+    if("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU" OR "${CMAKE_C_COMPILER_ID}" STREQUAL "Clang")
+        # We can't easily fix this at the source-code level, because the .c file is generated
+        # by the qaic program.  But it should be safe to ignore the warning:
+        # https://stackoverflow.com/questions/13905200/is-it-wise-to-ignore-gcc-clangs-wmissing-braces-warning
+        set_source_files_properties("${TVMRT_SOURCE_DIR}/hexagon/rpc/hexagon_rpc_stub.c"
+            PROPERTY COMPILE_FLAGS "-Wno-missing-braces")
+    endif()
   endfunction()
 
   if(BUILD_FOR_ANDROID)

src/runtime/hexagon/rpc/simulator/session.cc

@@ -466,6 +466,18 @@ std::string SimulatorRPCChannel::Cpu_::str() const {
   return default_cpu_;
 }
 
+// LOG(FATAL) always throws an exception or terminates the
+// process, but the compiler doesn't know that.
+#if (__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wreturn-type"
+#endif
+
+#if (__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wreturn-type"
+#endif
+
 std::string SimulatorRPCChannel::Message_::str() const {
   switch (msg.code) {
     case Message::kNone:
@@ -483,10 +495,19 @@ std::string SimulatorRPCChannel::Message_::str() const {
     case Message::kSendEnd:
       return "kSendEnd";
     default:
+      LOG(FATAL) << "Internal error: Unrecognized code value: " << msg.code;
       break;
   }
 }
 
+#if (__GNUC__)
+#pragma GCC diagnostic pop
+#endif
+
+#if (__clang__)
+#pragma GCC diagnostic pop
+#endif
+
 SimulatorRPCChannel::SDKInfo_::SDKInfo_(const std::string& sdk_root, const std::string& cpu)
     : root(sdk_root) {
   // For v69 chips, still look for v68 in the directory names.