[11u] 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

Anyone for this review?

Roland.