[lldb/lua] Suppress warnings about C-linkage in generated wrapper

[dim]

Summary

When lldb Lua bindings are enabled, the generated LLDBWrapLua.cpp file
generates a compiler warning about C-linkage:

lldb/LLDBWrapLua.cpp:71170:1: warning: 'LLDBSwigLuaBreakpointCallbackFunction' has C-linkage specified, but returns incomplete type 'llvm::Expected<bool>' which could be incompatible with C

In lldb/source/Plugins/ScriptInterpreter/Lua/Lua.cpp these warnings
are suppressed using a few pragmas. Also Add these to lua-wrapper.swig
so they end up in LLDBWrapLua.cpp, making the warnings disappear.

[JDevlieghere]

We should move this from the wrapper to the header block, similar to what Pavel did for Python: https://reviews.llvm.org/rG9a14adeae00015798843ff5cad987e5fdbdddb34

[dim]

In D115074#3170635, @JDevlieghere wrote:

We should move this from the wrapper to the header block, similar to what Pavel did for Python: https://reviews.llvm.org/rG9a14adeae00015798843ff5cad987e5fdbdddb34

I agree, but I'm not really qualified to do this. I just wanted to get rid of the warning. :)

[labath]

I just went ahead and did that in a52af6d3714.

lldb/bindings/lua/lua-wrapper.swig

 
 #ifdef __cplusplus
 }
 #endif
 %}
 
 %wrapper %{
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wreturn-type-c-linkage"
+
+// Disable warning C4190: 'LLDBSwigPythonBreakpointCallbackFunction' has
+// C-linkage specified, but returns UDT 'llvm::Expected<bool>' which is
+// incompatible with C
+#if _MSC_VER
+#pragma warning (push)
+#pragma warning (disable : 4190)
+#endif
+
 // This function is called from Lua::CallBreakpointCallback
 SWIGEXPORT llvm::Expected<bool>
 LLDBSwigLuaBreakpointCallbackFunction
 (
    lua_State *L,
    lldb::StackFrameSP stop_frame_sp,
    lldb::BreakpointLocationSP bp_loc_sp,
    StructuredDataImpl *extra_args_impl
)
 
    // Boolean return from the callback
    bool stop = lua_toboolean(L, -1);
    lua_pop(L, 1);
 
    return stop;
 }
 
+#if _MSC_VER
+#pragma warning (pop)
+#endif
+
+#pragma clang diagnostic pop
+
 SWIGEXPORT void
 LLDBSwigLuaCallLuaLogOutputCallback(const char *str, void *baton) {
    lua_State *L = (lua_State *)baton;
 
    lua_pushlightuserdata(L, (void *)&LLDBSwigLuaCallLuaLogOutputCallback);
    lua_gettable(L, LUA_REGISTRYINDEX);
 
    // FIXME: There's no way to report errors back to the user