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

hw/net/virtio-net.c

@@ -120,8 +120,8 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status)
         return;
     }
 
-    if (!!n->vhost_started ==
-        (virtio_net_started(n, status) && !nc->peer->link_down)) {
+    if ((virtio_net_started(n, status) && !nc->peer->link_down) ==
+        !!n->vhost_started) {
         return;
     }
     if (!n->vhost_started) {

kvm-all.c

@@ -366,7 +366,7 @@ static void kvm_log_stop(MemoryListener *listener,
     }
 }
 
-static int kvm_set_migration_log(int enable)
+static int kvm_set_migration_log(bool enable)
 {
     KVMState *s = kvm_state;
     KVMSlot *mem;

qemu-img.c

@@ -976,7 +976,8 @@ static int is_allocated_sectors_min(const uint8_t *buf, int n, int *pnum,
 static int compare_sectors(const uint8_t *buf1, const uint8_t *buf2, int n,
     int *pnum)
 {
-    int res, i;
+    bool res;
+    int i;
 
     if (n <= 0) {
         *pnum = 0;