specify timeout to solver on the command line
Roll LLVM to r213048

This incorporates a bug fix for the ExecuteAndWait function that fixed the
timeout functionality.

Also includes a number of API updates relating to the transition from
llvm::error_code to std::error_code in LLVM.
Merge pull request #23 from regehr/timeout

specify timeout to solver on the command line
fix a bug where the Clang pass aborts compilation upon solver timeout
Merge pull request #25 from regehr/timeout-fix

fix a bug where the Clang pass aborts compilation upon solver timeout