tsan: disable bench_threads.cpp on aarch64

The new test started failing on bots with:

CHECK failed: tsan_rtl.cpp:327 "((addr + size)) <= ((TraceMemEnd()))"
   (0xf06200e03010, 0xf06200000000) (tid=4073872)

https://lab.llvm.org/buildbot#builders/179/builds/1761

This is a latent bug in aarch64 virtual address space layout,
there is not enough address space to fit traces for all threads.
But since the trace space is going away with the new tsan runtime
(D112603), disable the test.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D113990

compiler-rt/test/tsan/bench_threads.cpp

@@ -4,6 +4,11 @@
 // bench.h needs pthread barriers which are not available on OS X
 // UNSUPPORTED: darwin
 
+// aarch64 fails with:
+// CHECK failed: tsan_rtl.cpp:327 "((addr + size)) <= ((TraceMemEnd()))"
+// TODO: try to re-enable when D112603 is landed.
+// XFAIL: aarch64
+
 #include "bench.h"
 
 void *nop_thread(void *arg) {