meson: Try building with -Wshorten-64-to-32

This adds a bunch more warnings, some similar to the ones produced
by MSVC by default.
18 jobs for master in 6 minutes and 38 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Style
passed #253050
amd64 debian
style-check

00:00:19

 
  Build
passed #253051
amd64 debian
build-debian

00:00:37

passed #253058
debian aarch64
build-debian-aarch64

00:01:24

passed #253059
debian aarch64
build-debian-aarch64-clang-5

00:01:02

passed #253062
debian armv7
build-debian-armv7

00:01:33

passed #253063
debian armv7
build-debian-armv7-clang-5

00:01:06

passed #253052
amd64 debian
build-debian-static

00:00:33

passed #253061
debian aarch64
build-debian-werror

00:00:33

passed #253053
amd64 debian
build-debian32

00:00:27

passed #253060
macos
build-macos

00:00:29

passed #253056
win32
build-win-arm32

00:00:28

passed #253057
win64
build-win-arm64

00:00:28

passed #253054
win32
build-win32

00:00:32

passed #253055
win64
build-win64

00:00:35

 
  Test
passed #253064
amd64 debian
test-debian

00:00:47

passed #253065
amd64 debian
test-debian-asan

00:02:02

passed #253066
amd64 debian
test-debian-msan

00:01:03

passed #253067
amd64 debian
test-debian-ubsan

00:01:23