nbd: disable signals and forking on Windows builds

Disabling these parts are sufficient to get the qemu-nbd program
compiling in a Windows build.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200825103850.119911-4-berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
diff --git a/qemu-nbd.c b/qemu-nbd.c
index dc6ef08..33476a1 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -899,6 +899,7 @@
 #endif
 
     if ((device && !verbose) || fork_process) {
+#ifndef WIN32
         int stderr_fd[2];
         pid_t pid;
         int ret;
@@ -962,6 +963,10 @@
              */
             exit(errors);
         }
+#else /* WIN32 */
+        error_report("Unable to fork into background on Windows hosts");
+        exit(EXIT_FAILURE);
+#endif /* WIN32 */
     }
 
     if (device != NULL && sockpath == NULL) {