Fix msvc and clang-msvc warnings with C++17

The codecvt header has been deprecatd for C++17, but no replacement has
been specified in the standard. It is possible to use the Windows
specific MultiByteToWideChar() and WideCharToMultiByte() from
<Windows.h> instead, however the codecvt header still works so there's
no reason to change it until a proper replacement has been specified in
the standard.

It is additionally necessary to manually set the standard for clang-msvc
to C++17.

advancedSettings.pro

@@ -22,6 +22,10 @@ TEMPLATE = app
     QMAKE_CXXFLAGS_WARN_ON -= -W3
     #C4127 was in a third party file with no way to turn off.
     QMAKE_CXXFLAGS += /W4 /wd4127
+    # The codecvt header being used in AudioManagerWindows.cpp is deprecated by the standard,
+    # but no suitable replacement has been standardized yet. It is possible to use the Windows
+    # specific MultiByteToWideChar() and WideCharToMultiByte() from <Windows.h>
+    DEFINES += _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
     !*clang-msvc {
         #win32-clang-msvc is unable to correctly build the first time
         #with warnings as errors on. There seems to be an issue with the moc_predefs.h
@@ -31,6 +35,10 @@ TEMPLATE = app
     }
 }
 
+win32-clang-msvc{
+    QMAKE_CXXFLAGS += /std:c++17
+}
+
 *g++* {
     QMAKE_CXXFLAGS += -Werror
 }