Had thought about it, short answer is it's more trouble than it's worth. Your suggestion still results in somewhat random locations being generated, that are extremely difficult to follow or predict where the absolute copied file will end up.

Based on the logs above, only two places even reference an absolute file in a copy operation, neither of which actually rely on the copied file for a build.

What this change introduces is three things:

1. Well-defined behaviour for an absolute file. It is copied into the _srcdir, with no extra "treats"
2. It no longer crashes the build on Windows
3. It no longer generates ridiculously nested folder structures for webversion.js on unix platforms.

To re-iterate, the patch builds an equivalently functional system on unix/linux/OSX as before, the only difference is the ignored absolute webversion.js file no longer appears nested a dozen levels deep. Now though, it also builds on Windows.

I'm trying to stop this PR getting side-tracked into solving the idea of whether absolute paths is a good idea or not, as without this patch, the argument is moot on Windows as a build cannot even be performed there.