Use <dir> for WINDOWSFONTDIR in Meson

Previous it created invalid config files because of this.
I noticed that `<dir>` in other parts of configuration so added this.
11 jobs for fix-config-files in 7 minutes and 34 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #7710965
meson android arm64 fedora

00:01:48

passed #7710963
gst-macos-10.15
meson macos

00:03:10

passed #7710960
meson-mingw-w64-build

00:04:42

manual #7710964
docker windows 1809 allowed to fail manual
meson msys2
passed #7710958
meson-shared-build

00:04:48

passed #7710959
meson-static-build

00:05:36

passed #7710961
docker windows 1809
meson vs2017 amd64

00:01:23

passed #7710962
docker windows 1809
meson vs2017 x86

00:01:22

passed #7710957
mingw-build

00:06:15

passed #7710955
shared-build

00:07:34

passed #7710956
static-build

00:06:18