attempt to fix more build failures against older Win32 SDKs.

src/filesystem/windows/SDL_sysfilesystem.c

@@ -30,6 +30,10 @@
 #include <initguid.h>
 
 /* These aren't all defined in older SDKs, so define them here */
+#ifndef DEFINE_KNOWN_FOLDER
+typedef GUID KNOWNFOLDERID;
+typedef KNOWNFOLDERID *REFKNOWNFOLDERID;
+#endif
 DEFINE_GUID(SDL_FOLDERID_Profile, 0x5E6C858F, 0x0E22, 0x4760, 0x9A, 0xFE, 0xEA, 0x33, 0x17, 0xB6, 0x71, 0x73);
 DEFINE_GUID(SDL_FOLDERID_Desktop, 0xB4BFCC3A, 0xDB2C, 0x424C, 0xB0, 0x29, 0x7F, 0xE9, 0x9A, 0x87, 0xC6, 0x41);
 DEFINE_GUID(SDL_FOLDERID_Documents, 0xFDD39AD0, 0x238F, 0x46AF, 0xAD, 0xB4, 0x6C, 0x85, 0x48, 0x03, 0x69, 0xC7);