bbmain: faster ResolveUntilLastSymlink

[dolmen]

In the main package of gobusybox binaries, reduce redundant calls to AbsSymlink in ResolveUntilLastSymlink.

This reduces string manipulations when resolving symlinks of os.Argv[0].

[rminnich]

This may well be an improvement but in the most common case, there is one symlink. In the outlier case there are 2. I'm not sure the performance benefit is worth the additional complexity.

[rminnich]

I do hope my review does not discourage you from contributing, I had not looked at the PRs for a while (I will do so more frequently) and missed this one.

I wonder if you could look at the many places in this tree that the go version is specified as go 1. and see if they should be brought up to date?

If you want to continue with this PR, I think we need more tests. This is code that must never break, as it is the core of the runtime, and I get worried about too much complexity.

Thank you.