xbyak: add int3 instruction

Very useful to stop the JIT

plugins/GSdx/xbyak/xbyak_mnemonic.h

@@ -370,6 +370,7 @@ void cwde() { db(0x98); }
 void lahf() { db(0x9F); }
 void lock() { db(0xF0); }
 void nop() { db(0x90); }
+void int3() { db(0xCC); }
 void sahf() { db(0x9E); }
 void stc() { db(0xF9); }
 void std() { db(0xFD); }