OS/2 Tinderbox break

Close but no cigar :) ndef XP_OS2 to avoid the DBCSLeadByte, but we need to avoid the windows.h include as well

xpinstall/src/nsRegisterItem.cpp

@@ -63,7 +63,7 @@ static void SwapSlashColon(char * s)
 } 
 #endif
 
-#ifdef XP_PC
+#if defined(XP_PC) && !defined(XP_OS2)
 #include <windows.h>
 #endif