debug info: use c++ namespace dwarf info to be able to see items in namespaces

[andrewrk]

test "MT19937 32" {
    const rng = MT19937_32.init(rand_test.mt32_seed);
    for (rand_test.mt32_data) |value| {
        assert(value == rng.get());
    }
}

192     const rng = MT19937_32.init(rand_test.mt32_seed);
(gdb) print rand_test.mt32_seed
No symbol "rand_test" in current context.

[andrewrk]

After recent changes, functions now have namespaces in their symbol name. However this proposal still might be a good idea. Related: #614