Reapply asan coverage changes 194702-194704.

I still don't know what is causing our bootstrapped LTO buildbots to fail,
but llvm r194701 seems to be OK and I can't imagine that these changes could
cause the problem.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@194790 91177308-0d34-0410-b5e6-96231b3b80d8