Add `MESON_ARGS` in activation script?

[munechika-koyo]

Hello!

Adding the definition of MESON_ARGS environmental variables like CMAKE_ARGS in the activation script seems to be useful to minimize build scripts and allow us to write them in a similar manner to Unix.

I would suggest that MESON_ARGS should include the following arguments at least:

set "MESON_ARGS=--prefix %LIBRARY_PREFIX% -Dbuildtype=release"

Note that I don't mean this in the cross-compiling context.

[isuruf]

Sure. PRs are welcome