[asan] initialize fake_stack_ to 0 before we call SetThreadStackAndTls, because that may actually try to use fake_stack_ (still don't know how). Yet another case where we desperately want https://sourceware.org/glibc/wiki/ThreadPropertiesAPI

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@210315 91177308-0d34-0410-b5e6-96231b3b80d8