tsan: move shadow stack from thread descriptors to fixed addresses

This allows to increase max shadow stack size to 64K,
and reliably catch shadow stack overflows instead of silently
corrupting memory.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192797 91177308-0d34-0410-b5e6-96231b3b80d8