ASSERT sigaction failure when DR run under QEMU emulating AArch64

We're seeing this assert at startup on sigaction failing when running DR under QEMU emulating AArch64 in user mode:

<Application xxx.  Internal Error: DynamoRIO debug check failure: dynamorio/trunk/core/unix/signal.c:1469 rc == 0 IF_VMX86(|| (sig >= 63 && rc == -EINVAL))
(Error occurred @0 frags)

I'll gather more info such as QEMU version, and try to repro with a standalone upstream QEMU.