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.
Add fixes for Win64
Add -L=-lcurl to std.net.curl unit test.

There is no pragma to pull in this library. Therefore specify the lib on the command line.
Also remove emptymain.d as we now have the -main switch.