meson: Use cmake to find LLVM when building windows

It might be better to have a command line option for this.

We don't use cmake normally because it always results in static linking.
This is very problematic for *nix OSes which expect shared linking by
default, but for windows this isn't a problem as LLVM doesn't support
shared linking on windows anyway.
14 jobs for !986 with meson-windows in 27 minutes and 18 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Containers Build
passed #448240
debian

00:18:27

 
  Build+Test
passed #448249
meson-arm64

00:03:55

passed #448248
meson-armhf

00:04:35

failed #448242
meson-clang

00:04:43

failed #448246
meson-clover

00:03:18

passed #448250
meson-i386

00:03:24

failed #448245
meson-main

00:06:12

failed #448251
meson-mingw

00:07:29

failed #448241
meson-swr-glvnd

00:07:20

failed #448247
meson-vulkan

00:02:54

passed #448253
scons-llvm

00:03:18

passed #448252
scons-nollvm

00:06:07

passed #448243
scons-swr

00:05:38

passed #448244
scons-win64

00:08:02

 
Name Stage Failure
failed
meson-mingw Build+Test
files in cache                      2689
cache size 130.4 MB
max cache size 5.0 GB
Uploading artifacts...
_build/meson-logs/*.txt: found 2 matching files
WARNING: _build/*/config.log: no matching files
WARNING: shader-db: no matching files
Uploading artifacts to coordinator... ok
id=448251 responseStatus=201 Created token=eiXCyM13
ERROR: Job failed: exit code 1
failed
meson-swr-glvnd Build+Test
files in cache                      4140
cache size 535.6 MB
max cache size 5.0 GB
Uploading artifacts...
_build/meson-logs/*.txt: found 2 matching files
WARNING: _build/*/config.log: no matching files
WARNING: shader-db: no matching files
Uploading artifacts to coordinator... ok
id=448241 responseStatus=201 Created token=yv5mNVKZ
ERROR: Job failed: exit code 1
failed
meson-main Build+Test
files in cache                      5343
cache size 356.8 MB
max cache size 5.0 GB
Uploading artifacts...
_build/meson-logs/*.txt: found 1 matching files
WARNING: _build/*/config.log: no matching files
WARNING: shader-db: no matching files
Uploading artifacts to coordinator... ok
id=448245 responseStatus=201 Created token=LGWZvMsb
ERROR: Job failed: exit code 1
failed
meson-clang Build+Test
files in cache                      1435
cache size 70.7 MB
max cache size 5.0 GB
Uploading artifacts...
_build/meson-logs/*.txt: found 1 matching files
WARNING: _build/*/config.log: no matching files
WARNING: shader-db: no matching files
Uploading artifacts to coordinator... ok
id=448242 responseStatus=201 Created token=Zsn7XaeD
ERROR: Job failed: exit code 1
failed
meson-clover Build+Test
files in cache                      2687
cache size 170.0 MB
max cache size 5.0 GB
Uploading artifacts...
_build/meson-logs/*.txt: found 1 matching files
WARNING: _build/*/config.log: no matching files
WARNING: shader-db: no matching files
Uploading artifacts to coordinator... ok
id=448246 responseStatus=201 Created token=C_mcvZtU
ERROR: Job failed: exit code 1
failed
meson-vulkan Build+Test
files in cache                      1163
cache size 54.7 MB
max cache size 5.0 GB
Uploading artifacts...
_build/meson-logs/*.txt: found 1 matching files
WARNING: _build/*/config.log: no matching files
WARNING: shader-db: no matching files
Uploading artifacts to coordinator... ok
id=448247 responseStatus=201 Created token=m9uxW-rJ
ERROR: Job failed: exit code 1