support build when moar's prefix ne target prefix

[kazcw]

Add a new config option, --with-moar-root=$DIR. This is necessary
to be able to build moar and nqp as separate NixOS packages.

[kazcw]

This is not sufficient. On unix install-moar-runner.pl still assumes moar and nqp are installed to the same directory.

[kazcw]

I think it'll be simpler to apply nix-specific patches than add the necessary knobs.

[niner]

But rakudo has supported different prefixes for MoarVM, NQP and rakudo for years via the --with-moar and --with-nqp options respectively?

[kazcw]

@niner I'm trying to create separate packages for moar and nqp (and later rakudo), so I can't make use of any rakudo options to get nqp to build. nqp has its own with-moar option, but that only sets the path to the moar binary, not the support files that go with it, which is what this PR was in reference to. What I ended up doing is adding a patch like this to enable configuring the location of the whole moar installation, and another patch to set $relocatable = 0 in install-moar-runner.pl, and I now have nqp successfully building against a moar in another directory.

[niner]

I've filed issues for both nqp and rakudo. This is clearly a regression that needs fixing before the next release.

[vrurg]

@kazcw From you mentioning install-moar-runner.pl I conclude that you're not working on master. The script is gone already.

[kazcw]

@vrurg I'm confused. I'm running de6e46c, which is currently the head of the branch called "master" in this repo. There's a file tools/build/install-moar-runner.pl: https://github.com/perl6/nqp/blob/master/tools/build/install-moar-runner.pl. It seems to be actively used, because by modifying it I can change the nqp and nqp-m scripts that get generated. Am I on the wrong master somehow?

[vrurg]

@kazcw That's my oops, I apologize for the confusion. While actively switching between nqp and rakudo builds I mixed them up and was speaking about rakudo at that moment.

[kazcw]

Oh that makes sense. I thought it seemed like we were talking about two different repos!