meson.build: define NOUSER on Windows for lighter windows.h

A few exceptions are needed for sources which include COM header
(directly or indirectly).

This fixes lots of shadow warnings, see
https://github.com/MusicPlayerDaemon/MPD/issues/1150

src/win32/Com.hxx

@@ -23,6 +23,7 @@
 #include "HResult.hxx"
 
 #include <combaseapi.h>
+#include <objbase.h> // for COINIT_APARTMENTTHREADED
 
 // RAII for Microsoft Component Object Model(COM)
 // https://docs.microsoft.com/en-us/windows/win32/api/_com/

src/win32/ComWorker.cxx

@@ -17,6 +17,8 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#undef NOUSER // COM needs the "MSG" typedef
+
 #include "ComWorker.hxx"
 #include "Com.hxx"
 #include "thread/Name.hxx"

src/win32/HResult.cxx

@@ -17,6 +17,11 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#ifdef _WIN32
+// COM needs the "MSG" typedef, and audiopolicy.h includes COM headers
+#undef NOUSER
+#endif
+
 #include "HResult.hxx"
 #include "system/Error.hxx"
 
@@ -25,6 +30,7 @@
 #include <cstdio>
 #include <memory>
 
+#include <combaseapi.h> // needed by audiopolicy.h if COM_NO_WINDOWS_H is defined
 #include <audiopolicy.h>
 
 std::string_view

src/win32/PropVariant.hxx

@@ -20,6 +20,7 @@
 #ifndef MPD_WIN32_PROPVARIANT_HXX
 #define MPD_WIN32_PROPVARIANT_HXX
 
+#include <combaseapi.h> // needed by propidl.h if COM_NO_WINDOWS_H is defined
 #include <propidl.h>
 
 class AllocatedString;