Add support for dynamic ASan runtime (on Linux) to Clang driver.

Based on http://llvm-reviews.chandlerc.com/D3043 by Yuri Gribov!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205310 91177308-0d34-0410-b5e6-96231b3b80d8