- mingw64 now links against SDL64.dll to allow for 32 and 64 bit version in the same directory

- Add library files for MinGW64

Makefile

@@ -562,8 +562,7 @@ ifeq ($(PLATFORM),mingw32)
                       $(LIBSDIR)/win32/libSDL.dll.a
     else
     CLIENT_LIBS += $(LIBSDIR)/win64/libSDLmain.a \
-                      $(LIBSDIR)/win64/libSDL.dll.a \
-                      $(LIBSDIR)/win64/libSDL.a
+                      $(LIBSDIR)/win64/libSDL64.dll.a
     endif
   else
     CLIENT_CFLAGS += $(SDL_CFLAGS)