tcg: Add TranslationBlock.jmp_insn_offset

Stop overloading jmp_target_arg for both offset and address,
depending on TCG_TARGET_HAS_direct_jump.  Instead, add a new
field to hold the jump insn offset and always set the target
address in jmp_target_addr[].  This will allow a tcg backend
to use either direct or indirect depending on displacement.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/exec/exec-all.h

@@ -587,7 +587,8 @@ struct TranslationBlock {
      */
 #define TB_JMP_OFFSET_INVALID 0xffff /* indicates no jump generated */
     uint16_t jmp_reset_offset[2]; /* offset of original jump target */
-    uintptr_t jmp_target_arg[2];  /* target address or offset */
+    uint16_t jmp_insn_offset[2];  /* offset of direct jump insn */
+    uintptr_t jmp_target_addr[2]; /* target address */
 
     /*
      * Each TB has a NULL-terminated list (jmp_list_head) of incoming jumps.