[Sanitizer] Move lit config for sanitizer_common unit tests under Unit/ dir for consistency.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208373 91177308-0d34-0410-b5e6-96231b3b80d8
[Sanitizer] Add the machinery to run the same test under several sanitizers

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208378 91177308-0d34-0410-b5e6-96231b3b80d8