midenc option `--emit hir=./target` does not emit when passed along with `-o`

[greenhat]

Discovered while working on #723

When running cargo miden build --release --emit hir=./target the --emit option is overridden by -o. The run finishes with error compilation was canceled by user(which is suspicious) but the Miden package is created.

The midenc arguments passed in this case are:

    "--output-dir",
    "/Users/green/src/miden/compiler/examples/basic-wallet/target/miden/release",
    "-o",
    "/Users/green/src/miden/compiler/examples/basic-wallet/target/miden/release/basic_wallet.masp",
    "--verbose",
    "--target",
    "rollup:account",
    "--lib",
    "--emit",
    "hir=./target",

[bitwalker]

That's odd - -o should only be overriding the output path for the masp output type, and only if the masp output type was requested by --emit, all other output types should be left alone.

In the example above, I'd expect the following:

• The --emit flag only requests HIR, not any link artifacts, so we never get to the point where the output file is written, so whether or not -o is provided doesn't change anything
• Since --emit is specified, but the masp type is not requested, the -o flag is going to be ignored entirely
• If you had instead specified --emit hir=./target,link, then I'd expect the -o option to override the path to which the masp artifact is written, while leaving the hir output path unmodified.
• If you had been even more explicit, and passed --emit hir=./target,link=foo.masp (i.e. the path specified to --emit conflicts with -o for the masp output type), the -o option should take precedence

It isn't clear to me how we're writing the masp file at all, unless we're erroneously checking if output_file was set when determining the outcome of should_link.