Set source character sets to UTF-8

This suppress warning C4819.
https://docs.microsoft.com/en-us/cpp/build/reference/utf-8-set-source-and-executable-character-sets-to-utf-8?view=msvc-160

cmake/Modules/MacroQbtCommonConfig.cmake

@@ -70,8 +70,12 @@ macro(qbt_common_config)
     endif()
 
     if (MSVC)
-        target_compile_options(qbt_common_cfg INTERFACE /guard:cf)
-        target_link_options(qbt_common_cfg INTERFACE /guard:cf
+        target_compile_options(qbt_common_cfg INTERFACE
+            /guard:cf
+            /utf-8
+        )
+        target_link_options(qbt_common_cfg INTERFACE
+            /guard:cf
             $<$<NOT:$<CONFIG:Debug>>:/OPT:REF /OPT:ICF>
             # suppress linking warning due to /INCREMENTAL and /OPT:ICF being both ON
             $<$<CONFIG:RelWithDebInfo>:/INCREMENTAL:NO>

src/base/unicodestrings.h

@@ -1,4 +1,4 @@
-/*
+/*
  * Bittorrent Client using Qt and libtorrent.
  * Copyright (C) 2015  Mike Tzou
  *
@@ -28,11 +28,6 @@
 
 #pragma once
 
-// This file must be encoded in "UTF-8 with BOM"
-#ifdef _MSC_VER
-#pragma execution_character_set("utf-8")
-#endif
-
 // Because of the poor handling of UTF-8 characters in MSVC (emits warning C4819),
 // we put all problematic UTF-8 chars/strings in this file.
 // See issue #3059 for more details (https://github.com/qbittorrent/qBittorrent/issues/3059).

winconf.pri

@@ -40,7 +40,7 @@ win32-g++* {
 }
 else:win32-msvc* {
     CONFIG -= embed_manifest_exe
-    QMAKE_CXXFLAGS += /std:c++17
+    QMAKE_CXXFLAGS += /std:c++17 /utf-8
     QMAKE_LFLAGS += "/MANIFEST:EMBED /MANIFESTINPUT:$$quote($${PWD}/src/qbittorrent.exe.manifest) /STACK:0x800000"
 
     RC_FILE = qbittorrent.rc