`--fetch` flag now has additional optional parameter, which specifies
how lazy dependencies should be fetched:
* `needed` — lazy dependencies are fetched only if they are required
for current build configuration to work. Default and works same
as old `--fetch` flag.
* `all` — lazy dependencies are always fetched. If `--system` flag
is used after that, it's guaranteed that **any** build configuration
will not require additional download of dependencies during build.
Helpful for distro packagers and CI systems:
https://www.github.com/ziglang/zig/issues/14597#issuecomment-1426827495
If none is passed, behaviour is same as if `needed` was passed.
Signed-off-by: Eric Joldasov <bratishkaerik@landless-city.net>