[8u] RFR 8231430: C2: Memory stomp in max_array_length() for T_ILLEGAL type

[Aleksey Shipilev]

Original bug:
  https://bugs.openjdk.java.net/browse/JDK-8231430
  https://hg.openjdk.java.net/jdk/jdk/rev/54af3178cdbd

This is one nasty bug, and it affects 8u as well. Unfortunately, it does not apply cleanly due to
context changes. Also, it misses the introduction of is_reference_type helper (part of much larger
JDK-8230505), and the fatal needs to be wrapped in err_msg to match the old signature.

8u webrev:
  https://cr.openjdk.java.net/~shade/8231430/webrev.8u.01/

Testing: tier1

-- 
Thanks,
-Aleksey