meson: Specify encoding to UTF-8 when building with MSVC

Use build arguments consistent with core and -base. This can also
remove noisy "C4819" warning of non-us locale MSVC.
3 jobs for fix-c4819-warning in 6 minutes and 58 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #48838
manifest

00:00:21

 
  Build
passed #48839
build fedora x86_64

00:03:27

 
  Full Builds
passed #48840
build android arm64 api28

00:03:09