Make sure to zero out memory before calling madvise to increase robustness

Avi pointed out that it's not entirely safe to rely on madvise zeroing out
memory.  So let's do it explicitly before calling madvise.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

vl.c

@@ -3358,13 +3358,13 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
         
         if (flags & RAM_SAVE_FLAG_COMPRESS) {
             uint8_t ch = qemu_get_byte(f);
-#if defined(__linux__)
+            memset(qemu_get_ram_ptr(addr), ch, TARGET_PAGE_SIZE);
+#ifndef _WIN32
             if (ch == 0 &&
                 (!kvm_enabled() || kvm_has_sync_mmu())) {
                 madvise(qemu_get_ram_ptr(addr), TARGET_PAGE_SIZE, MADV_DONTNEED);
-            } else
+            }
 #endif
-            memset(qemu_get_ram_ptr(addr), ch, TARGET_PAGE_SIZE);
         } else if (flags & RAM_SAVE_FLAG_PAGE)
             qemu_get_buffer(f, qemu_get_ram_ptr(addr), TARGET_PAGE_SIZE);
     } while (!(flags & RAM_SAVE_FLAG_EOS));