After reading the dependency file, ninja just deletes it, in the name
of cleanliness I guess.  However this complicates debugging unnecessarily
compared to good old "-include *.d".  Use the keepdepfile debugging
option to make it easier to see what is going on.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210215122103.63933-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>