configure: default to PIE disabled on Windows platforms

configure: default to PIE disabled on Windows platforms

If Windows EXE files are built with -pie/-fpie they will fail to
launch. Historically QEMU defaulted to disabling PIE for Windows,
but this setting was accidentally lost when the configure summary
text was removed in

  commit f9332757898a764d85e19d339ec421236e885b68
  Author: Paolo Bonzini <pbonzini@redhat.com>
  Date:   Mon Feb 3 13:28:38 2020 +0100

    meson: move summary to meson.build

    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Fixes: f9332757898a764d85e19d339ec421236e885b68
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>