Make function entry basic blocks unnamed.

The performance impact should be completely immeasurable,
but the main benefit is that this makes IR dumps slightly
nicer to look at (as the redundant "empty:" labels are
now omitted entirely).
Merge pull request #653 from klickverbot/unnamed-entry-bb

Make function entry basic blocks unnamed.
Remove unused 'seenTemplateInstances' mechanism.
Use --gc-sections on Linux.

This was painful.