Use CXX Unicode flags for FTXUI on Windows

Author: Sunrisepeak

pkgs/c/compat.ftxui.lua

@@ -52,7 +52,7 @@ package = {
         targets = { ["ftxui"] = { kind = "lib" } },
         deps    = { },
         windows = {
-            cflags = { "-DUNICODE", "-D_UNICODE" },
+            cxxflags = { "-DUNICODE", "-D_UNICODE" },
         },
     },
 }