CRASH ASSERT running shell script on ARM

Using latest trunk. Running on Ubuntu 18.04 on Arm (32-bit on a Neoverse N1 platform). Trying to run Firefox. /usr/bin/firefox is a shell script so /bin/dash is invoked. DR can normally run /bin/dash but not in this case. It crashes with a backtrace. There's also a "Not tested" message printed (with the debug build) from emit_special_ibl_xfer.
```
../dynamorio/build.dbg/bin32/drrun -- /bin/dash -c /usr/bin/firefox
```
output:
```

<(1+x) Handling our fault in a TRY at 0x711edfe4>
<-- parent 15703 forked child 15704 -->
<-- execve /bin/sh -->

<(1+x) Handling our fault in a TRY at 0x711edfe4>
<-- parent 15704 forked child 15705 -->
<-- execve /bin/sh -->

<(1+x) Handling our fault in a TRY at 0x711edfe4>

```