Order of --output-directory flag matters

[gergoerdi]

The following invocation of ahc-link puts (most) generated files into _build/:

ahc-link --input-hs src/main.hs --output-directory _build

However, passing the output-directory flag earlier seems to be ignored, as the following invocation puts everything into src/:

ahc-link --output-directory _build --input-hs src/main.hs