This patch exposes to Clang users three more sanitizers are experimental features...

This patch exposes to Clang users three more sanitizers are experimental features of ASan:
1) init-order sanitizer: initialization-order checker.
Status: usable, but may produce false positives w/o proper blacklisting.
2) use-after-return sanitizer
Status: implemented, but heavily understed.
Should be optional, as it significanlty slows program down.
3) use-after-scope sanitizer
Status: in progress.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168950 91177308-0d34-0410-b5e6-96231b3b80d8