RFR: 8338158: Cleanup ShouldNotXXX uses in machnode.cpp

[Dean Long]

On Mon, 12 Aug 2024 07:23:57 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to machnode.cpp to remove dead code following calls
> to ShouldNotReachHere() and ShouldNotCallThis().  This takes advantage of the
> availability and use of [[noreturn]] attributes on all supported platforms,
> and makes all uses of those functions in this file consistent in this respect.
> 
> As a side effect, this removes some -Wzero-as-null-pointer-constant warnings.
> 
> Testing: mach5 tier1

Marked as reviewed by dlong (Reviewer).

-------------

PR Review: https://git.openjdk.org/jdk/pull/20540#pullrequestreview-2234423646