merge mesa 21.3.7.

Add workaround for non-zero initialized initial-exec TLS variables.
NetBSD doesn't support these with dlopen.

Ref:
https://bugs.freedesktop.org/show_bug.cgi?id=35268
https://mail-index.netbsd.org/pkgsrc-users/2015/09/11/msg022180.html
http://gnats.netbsd.org/50277

Fixes dlopen of libGL reported by prlw1 on current users.
From tnn, via pkgsrc/graphics/MesaLib*.

from maya:

Import mesa 18.3.4.

Mesa 18.3.4 implements the OpenGL 4.5 API.
Some drivers don't support all the features required in OpenGL 4.5.

initial import of MesaLib-10.3.5