Fix adding module arguments for Step.Compile

[PanSashko]

The existing implementation adds the same module multiple times in the following case:

1. Module app depends on the static library lib and the module mod.

// file: app/build.zig.zon
.{
    .name = "app",
    .version = "0.0.0",
    .dependencies = .{
        .lib = .{ .path = "../lib", },
        .mod = .{ .path = "../mod", },
    },
    .paths = .{ "" },
}

2. Static library lib depends on the module mod too.

// file: lib/build.zig.zon
.{
    .name = "lib",
    .version = "0.0.0",
    .dependencies = .{
        .mod = .{ .path = "../mod", },
    },
    .paths = .{ "" },
}

The build fails with

error: error: unable to add module 'mod': already exists as 'mod.zig'

This PR fixed the above problem.

According to my limited understanding of the convoluted Zig build system, the proposed fix should not break any other uses of build dependencies.

[PanSashko]

Sorry for recreating the PR. I used the master branch in my fork by mistake, and GitHub closes the PR on the master branch sync.

[PanSashko]

The test revealed another bug:

no dependency named 'mod' in '/home/ci/actions-runner1/_work/zig/zig/test/standalone/dep_duplicate_module/build.zig.zon'. All packages used in build.zig must be declared in this file

Manual build of the test "project" passes. The bug might be related to Builder.createChild(...).

I simplified the test to avoid using build.zig.zon. It should work now.

[andrewrk]

Thank you