hwasan: Move stack ring buffer initialization before InitStackAndTls.

[pcc]

Summary

D104248 moved the call to GetThreadStackAndTls to before the
initialization of the ring buffer TLS slot. As a result, if libc
is instrumented we crash in pthread_getattr_np which is called from
__sanitizer::GetThreadStackTopAndBottom.

Fix the problem by moving the stack ring buffer initialization before
the call to InitStackAndTls.

[eugenis]

LGTM

compiler-rt/lib/hwasan/hwasan_thread.cpp

void Thread::Init(uptr stack_buffer_start, uptr stack_buffer_size,
   CHECK_EQ(0, stack_top_);
   CHECK_EQ(0, stack_bottom_);
 
   static u64 unique_id;
   unique_id_ = unique_id++;
   if (auto sz = flags()->heap_history_size)
     heap_allocations_ = HeapAllocationsRingBuffer::New(sz);
 
-  InitStackAndTls(state);
 #if !SANITIZER_FUCHSIA
   // Do not initialize the stack ring buffer just yet on Fuchsia. Threads will
   // be initialized before we enter the thread itself, so we will instead call
   // this later.
   InitStackRingBuffer(stack_buffer_start, stack_buffer_size);
 #endif
+  InitStackAndTls(state);
 }
 
 void Thread::InitStackRingBuffer(uptr stack_buffer_start,
                                  uptr stack_buffer_size) {
   HwasanTSDThreadInit();  // Only needed with interceptors.
   uptr *ThreadLong = GetCurrentThreadLongPtr();
   // The following implicitly sets (this) as the current thread.
   stack_allocations_ = new (ThreadLong)