meson: favor _aligned_malloc over posix_memalign

posix_memalign is defined as a built-in in gcc in msys2 but it's not available
when linking with the Universal C Runtime. _aligned_malloc is available in the
UCRT.

That should only affect builds targeting Windows since _aligned_malloc is a MS
thing.
33 jobs for posix_memalign in 3 minutes and 42 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Style
passed #398395
amd64 docker
style-check

00:00:15

 
  Build
passed #398406
amd64 docker
build-android-aarch64

00:00:19

passed #398405
amd64 docker
build-android-armv7

00:00:19

passed #398396
amd64 avx2 docker
build-debian

00:00:26

passed #398407
aarch64 docker
build-debian-aarch64

00:01:15

passed #398408
aarch64 docker
build-debian-aarch64-clang-5

00:00:56

passed #398411
armv7 docker
build-debian-armv7

00:00:47

passed #398412
armv7 docker
build-debian-armv7-clang-5

00:00:40

passed #398399
amd64 docker
build-debian-examples

00:00:29

passed #398414
ppc64le docker
build-debian-ppc64le

00:01:34

passed #398397
amd64 docker
build-debian-static

00:00:30

passed #398410
aarch64 docker
build-debian-werror

00:00:34

passed #398398
amd64 docker
build-debian32

00:00:26

passed #398409
macos
build-macos

00:00:31

passed #398415
amd64 docker
build-pages

00:00:13

passed #398413
amd64 docker
build-ubuntu-snap

00:00:26

passed #398403
amd64 docker
build-win-arm32

00:00:20

passed #398404
amd64 docker
build-win-arm64

00:00:19

passed #398400
amd64 docker
build-win32

00:00:31

passed #398401
amd64 docker
build-win32-unaligned-stack

00:00:30

passed #398402
amd64 docker
build-win64

00:00:33

 
  Test
passed #398416
amd64 docker
test-debian

00:00:34

passed #398425
aarch64 docker
test-debian-aarch64

00:02:09

passed #398427
armv7 docker
test-debian-armv7-clang-5

00:02:13

passed #398421
amd64 docker
test-debian-asan

00:01:33

passed #398417
avx2 amd64 docker
test-debian-asm

00:00:57

passed #398422
amd64 docker
test-debian-msan

00:00:43

passed #398419
amd64 docker
test-debian-mt

00:00:38

passed #398426
ppc64le docker
test-debian-ppc64le

00:01:38

passed #398423
amd64 docker
test-debian-ubsan

00:01:15

passed #398420
amd64 avx2 docker
test-debian-unaligned-stack

00:00:35

passed #398418
avx2 amd64 docker
test-debian32-asm

00:00:59

passed #398424
amd64 avx2 docker
test-win64

00:00:46