[ASan] Fix a couple of nits in NULL deref tests

This is a follow-up to r212807

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@212943 91177308-0d34-0410-b5e6-96231b3b80d8
[tsan] add a currently-failing test with a must-deadlock

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@212944 91177308-0d34-0410-b5e6-96231b3b80d8