merge mesa 19.1.7 into MesaLib.old.

initial import of Mesa 19.1.7 into MesaLib.old.

spell it defined(__NetBSD__) so it actually matches and we skip this
pragma warning during the build:

Warning: Per application configuration won't work with your OS version.

import the existing Mesa 10.x sources as MesaLib.old while we
handle the upgrade to Mesa 18.x.