RFR: Make compile on other platforms.

[Coleen Phillimore]

On Mon, 21 Mar 2022 21:39:56 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This patch with additions and deletions of dummy stubs gets loom to compile on zero, ppc, s390, arm, linux 32 bit open, ie platforms that Oracle doesn't support.
> There are two not nice 
> #if !defined(AMD64) || !defined(AARCH64) || defined(ZERO)
> changes.  One for platform dependent code in signature.cpp and the other is because linux zero product inlining detects the dummy null return as input to memcpy.
> Also has a stack walking change that makes zero not complete compilation with the built compiler because of dummy returns.  Removing this doesn't cause any test failures in the loom tier1-3 code.

Thanks Alan.

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PR: https://git.openjdk.java.net/loom/pull/111