tcg: try sti when moving a constant into a dead memory temp

tcg: try sti when moving a constant into a dead memory temp

This comes from free from unifying tcg_reg_alloc_mov and
tcg_reg_alloc_movi's handling of TEMP_VAL_CONST.  It triggers
often on moves to cc_dst, such as the following translation
of "sub $0x3c,%esp":

  before:                          after:
  subl   $0x3c,%ebp                subl   $0x3c,%ebp
  movl   %ebp,0x10(%r14)           movl   %ebp,0x10(%r14)
  movl   $0x3c,%ebx                movl   $0x3c,0x2c(%r14)
  movl   %ebx,0x2c(%r14)

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1473945360-13663-1-git-send-email-pbonzini@redhat.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>