JDK-8230594 introduced use of:

  void add_target_count(int count) { Atomic::add(&_pending_threads, count); }

That's an atomic add on int64_t value. This fails to compile on 32-bit (ARM) with:

src/hotspot/share/runtime/atomic.hpp:741: error: undefined reference to 'long long Atomic::PlatformAdd<8u>::add_and_fetch<long long, long long>(long long volatile*, long long, atomic_memory_order) const'
collect2: error: ld returned 1 exit status