fix GCC 5.0.0 logical-not-parentheses warnings

fix GCC 5.0.0 logical-not-parentheses warnings

man gcc:
  Warn about logical not used on the left hand side operand of a
  comparison.  This option does not warn if the RHS operand is of a
  boolean type.

By preferring bool over int where sensible, but without modifying any
depending code, make GCC happy in cases like this,
  qemu-img.c: In function ‘compare_sectors’:
  qemu-img.c:992:39: error: logical not is only applied to the left hand
  side of comparison [-Werror=logical-not-parentheses]
           if (!!memcmp(buf1, buf2, 512) != res) {

hw/ide/core.c:1836 doesn't throw an error,
  assert(!!s->error == !!(s->status & ERR_STAT));
even thought the second operand is int (and first hunk of this patch has
a very similar case), maybe GCC developers still have a little faith in
C programmers.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>