I have a project where the file with the entry point is not at the root of the src directory, where I have everything else. Previously, on addExecutable I could pass the main_mod_path argument to be src/ and that would allow me to @import a file src/foo/bar.zig from src/baz/main.zig, for instance (as ../foo/bar.zig). However, the main_mod_path option, was removed in c20ad5. Reading through the diff, I can see the deletion but no similar option added.
And no, it's not an option to put main.zig directly on src/ (or something to avoid, rather), as it's a low-level project that needs different entry points depending on the architecture.