Fix or add missing premake workaround

[danielappelt]

No description provided.

[falkTX]

Thanks, but this is not quite right.
it should set PREMAKE var only if it is not in the path, so you can do instead something like:

if ! which premake > /dev/null; then
    if [ ! -f premake ]; then
        wget ...
    fi
    PREMAKE=...
fi

[danielappelt]

Thank you for your feedback. I just applied the same logic as is currently present in distrho-ports-labs. Does it need to be changed there too (and possibly for other plugins that use the same patch)? It worked just fine here with the given commit..

[danielappelt]

The pull request now covers all premake patches. @falkTX, could you check again?