sort-of-fix Mesa on most 32-bit platforms.

the new sparse_array implementation in Mesa 21 (not present in Mesa 19,
as shipped with netbsd-10) triggers it asking for an __atomic_load_8()
function, alongside it's __atomic_fetch_add_8/__atomic_fetch_sub_8/
__sync_val_compare_and_swap_8 versions on 32-bit platforms, so add a
__atomic_load_8() workaround that uses the same method as the others
to provide sync. (i did check, and almost the accesses in mesa that
this accessor is used with do go via the API, the only ones not used
are as part setup/clean up.

tested by rin@ on macppc.

try again to get it working for clang

fix for clang.

use long long and volatile consistently.

merge Mesa 18.3.4.

this work is mostly from maya@ with a little help from myself
via these github commits:


commit 57df9d9b59df14fd6ac8e30832ce4f29572a33c0
Author: coypu <coypu@sdf.org>
Date: Mon Mar 4 12:24:37 2019 +0200

Make GCC happier about prototype, include right header for __HAVE_ATOMIC64_OPS

commit 93c2f416aa316cc3d0665661c9f927f6949cdd37
Author: coypu <coypu@sdf.org>
Date: Mon Mar 4 12:16:56 2019 +0200

Make the u_atomic.c fallback locked 64bit atomics more suited

for the netbsd case: we are using __GNUC__ compilers, but without
libatomic. so we are emitting the __GNUC__ names.

Use __HAVE_ATOMIC64_OPS which is the netbsd name for this condition
(we don't run configure)

commit 84c2bf2f622f8a78f68ad1ca35b90bb991bdaab0
Author: coypu <coypu@sdf.org>
Date: Sun Mar 3 20:02:38 2019 +0200

Remove unused padding to struct.

The extra space is in the flexible array member at the end of
struct drm_i915_query_topology_info.

Clang dislikes having an extra member to the struct after the flexible
array member.

commit 00f432b0edf95a6e292e8259ad3096a07966b53c
Author: Maya Rashish <maya@NetBSD.org>
Date: Sun Feb 24 23:36:09 2019 +0200

Avoid left-shifting a negative, for clang

commit 84881d47e674b93b79f405326b3ae43af53fe611
Author: Maya Rashish <maya@NetBSD.org>
Date: Sun Feb 24 21:30:43 2019 +0200

avoid conflict with netbsd bswap32

commit d9bd43728cb5cf161d8501be6d53dee50f094df0
Author: Maya Rashish <maya@NetBSD.org>
Date: Sun Feb 24 21:30:30 2019 +0200

cast enum to appease clang

commit a84ec26c89d08028800e74313ccbbf0a1a0753ed
Author: Maya Rashish <maya@NetBSD.org>
Date: Wed Feb 6 13:07:55 2019 +0200

Apply patches from pkgsrc mesa to avoid atexit on a library.

This isn't safe to do on netbsd and results in segfaults on
program exit.

commit 335ea9c725374db31fe809a7d7f33ad8a83edd3e
Author: Maya Rashish <maya@NetBSD.org>
Date: Sat Jan 19 16:32:28 2019 +0200

Avoid left-shifting a negative (UB), appeases clang

commit 452e5dc79ee89292fe771cf0e1066d1fad55adfa
Author: Maya Rashish <maya@NetBSD.org>
Date: Sat Jan 12 17:02:04 2019 +0200

radeon picture_type is h264 and the enums match, cast to avoid

clang warning (we use -Werror)

commit 61b4bc2f7ca8d78bd4092df76daeb27621d2ea7d
Author: Maya Rashish <maya@NetBSD.org>
Date: Fri Jan 11 19:57:34 2019 +0200

Avoid redefinition, for clang.

commit c73fac417444cd79ee5a7a89b4a0fdf931e5122d
Author: Maya Rashish <maya@NetBSD.org>
Date: Sun Jan 6 19:52:12 2019 +0200

Fix some printf specifiers.

XXX more upstreaming
radeon_dma.c: https://gitlab.freedesktop.org/mesa/mesa/merge_requests/68

commit 09341f929e9d3b03a3caacaa630521bc76680344
Author: Maya Rashish <maya@NetBSD.org>
Date: Sat Feb 23 11:51:50 2019 +0200

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.