Looks OK and reasonably safe, although there have been times that I've installed LSST prerequisites in my own directories. I don't think they've been apr prerequisites, though, so this should still work.

I just realized that this may cause problems with devtoolset and other toolchains that modify PATH. I understand that Gabriele Comoretto [X] also discovered that and is working on a fix.

The devtoolset location should be now properly taken in account.

I think this is sufficient for now, given that we're hoping to replace this build method altogether. Otherwise, I'd still be worried that some environments would not be accommodated by this.

Changes merged into master and 1.5.4.lsst1 tag created