[Sanitizer] Make SuppressionContext a singleton class, residing in sanitizer_common.

Convert TSan and LSan to the new interface. More changes will follow:
1) "suppressions" should become a common runtime flag.
2) Code for parsing suppressions file should be moved to SuppressionContext::Init().


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@214334 91177308-0d34-0410-b5e6-96231b3b80d8