thread local data, embed them in the class using a uint64_t and make sure
we get compiler errors if there's a platform where this is not big enough.
This makes ThreadLocal more safe for using it in conjunction with CrashRecoveryContext.
Related to crash in rdar://11434201.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158342 91177308-0d34-0410-b5e6-96231b3b80d8