[PATCH] Implement argv0-less getMainExecutable for FreeBSD

[Ed Maste]

> I would prefer using dl_iterate_phdr for this, I think.

Ahh, good point - for some reason I thought it did not include the executable itself, but a quick test confirms it behaves as expected on FreeBSD stable/10 at least.  That said, I don't see a guarantee that the first result returned is the executable.

http://reviews.llvm.org/D5693