klee: let user override path to runtime library

Hi,

recently I've run into this very same problem:
http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-June/062731.html

My use-case is that I'd like to run klee in parallel  on more computers, but I don't want to build it in place, but rather to rsync it there (just the binary and related libs). The hard-coded paths do a little bit mess in it.

I solved it by this patch for now. Do you think something like this could be accepted upstream?

Thanks,
Marek