Ignore clang warnings on anon structs and uninons

Ignore the clang -Wc11-extensions warnings on the anonymouns struct and
union in Dav1dWarpedMotionParams.

include/dav1d/headers.h is a public header. Therefore, it is also
compiled by build systems of dav1d clients, which may use C99 and have
the clang -Wc11-extensions warnings enabled.
33 jobs for patch-7 in 3 minutes and 34 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Style
passed #425412
amd64 docker
style-check

00:00:14

 
  Build
passed #425423
amd64 docker
build-android-aarch64

00:00:18

passed #425422
amd64 docker
build-android-armv7

00:00:23

passed #425413
amd64 avx2 docker
build-debian

00:00:31

passed #425424
aarch64 docker
build-debian-aarch64

00:01:08

passed #425425
aarch64 docker
build-debian-aarch64-clang-5

00:00:59

passed #425428
armv7 docker
build-debian-armv7

00:00:46

passed #425429
armv7 docker
build-debian-armv7-clang-5

00:00:40

passed #425416
amd64 docker
build-debian-examples

00:00:26

passed #425431
ppc64le docker
build-debian-ppc64le

00:01:21

passed #425414
amd64 docker
build-debian-static

00:00:31

passed #425427
aarch64 docker
build-debian-werror

00:00:35

passed #425415
amd64 docker
build-debian32

00:00:31

passed #425426
macos
build-macos

00:00:37

passed #425432
amd64 docker
build-pages

00:00:16

passed #425430
amd64 docker
build-ubuntu-snap

00:00:27

passed #425420
amd64 docker
build-win-arm32

00:00:18

passed #425421
amd64 docker
build-win-arm64

00:00:24

passed #425417
amd64 docker
build-win32

00:00:39

passed #425418
amd64 docker
build-win32-unaligned-stack

00:00:34

passed #425419
amd64 docker
build-win64

00:00:50

 
  Test
passed #425433
amd64 docker
test-debian

00:00:57

98.2241%
passed #425442
aarch64 docker
test-debian-aarch64

00:02:08

passed #425444
armv7 docker
test-debian-armv7-clang-5

00:00:51

passed #425438
amd64 docker
test-debian-asan

00:01:26

passed #425434
avx2 amd64 docker
test-debian-asm

00:00:54

passed #425439
amd64 docker
test-debian-msan

00:00:52

passed #425436
amd64 docker
test-debian-mt

00:00:39

passed #425443
ppc64le docker
test-debian-ppc64le

00:01:43

passed #425440
amd64 docker
test-debian-ubsan

00:00:59

passed #425437
amd64 avx2 docker
test-debian-unaligned-stack

00:00:39

passed #425435
avx2 amd64 docker
test-debian32-asm

00:00:56

passed #425441
amd64 avx2 docker
test-win64

00:01:00