Thumb2 overestimates size of COND_EXEC insns

This piece of code

/* Add two bytes to the length of conditionally executed Thumb-2
   instructions for the IT instruction. */
#define ADJUST_INSN_LENGTH(insn, length) \
  if (TARGET_THUMB2 && GET_CODE (PATTERN (insn)) == COND_EXEC) \
    length += 2;

causes us to overestimate the length of COND_EXEC blocks with more than one conditional instruction. It would be better to add a pass to arm_reorg that adds unspec_volatile IT insns which have length 2.

[CodeSourcery Tracker ID #8452]