tsan: fix scanf interceptor


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@191445 91177308-0d34-0410-b5e6-96231b3b80d8
tsan: support allocator_may_return_null flag
Fixes https://code.google.com/p/thread-sanitizer/issues/detail?id=29



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@191482 91177308-0d34-0410-b5e6-96231b3b80d8