meson: prevent memory sanitizer builds with asm

For example in dav1d_cdef_brow_{8,10}bpc memory sanitizer can not track
that variance is initilized by dsp->cdef.dir() it is implemented by in
asm.
9 jobs for master in 2 minutes and 46 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #34578
amd64 debian
build-debian

00:00:30

passed #34582
debian aarch64
build-debian-aarch64

00:01:42

passed #34583
debian clang5 aarch64
build-debian-aarch64-clang-5

00:01:13

passed #34579
amd64 debian
build-debian-static

00:00:31

passed #34585
debian aarch64
build-debian-werror

00:00:54

passed #34584
macos
build-macos

00:00:26

passed #34580
win32
build-win32

00:00:28

passed #34581
win64
build-win64

00:00:33

 
  Test
passed #34586
amd64 debian
test-debian

00:00:36