8217230: assert(t == t_no_spec) failure in NodeHash::check_no_speculative_types()

[Roland Westrelin]

This is required to backport 8237086 (assert(is_MachReturn()) running
CTW with fix for JDK-8231291).

Original bug:
  https://bugs.openjdk.java.net/browse/JDK-8217230
  http://hg.openjdk.java.net/jdk/jdk12/rev/1b292ae4eb50

Original patch does not apply cleanly to 11u because context changed in
compile.hpp. Patch is otherwise identical.

11u webrev:
  http://cr.openjdk.java.net/~roland/8217230.11u/webrev.00/

Testing: x86_64 build, tier1 + tier2

Roland.