RFR: 8248188: Add HotSpotIntrinsicCandidate and API for Base64 decoding

[CoreyAshford]

On Tue, 29 Sep 2020 16:39:25 GMT, CoreyAshford <github.com+51754783+CoreyAshford at openjdk.org> wrote:

> Did you try on x86? AOT is not supported on PPC64.

After looking at this a bit, I find that there seems to be an assumption in the code that if there is an intrinsic
symbol defined in aotCodeHeap.cpp using the SET_AOT_GLOBAL_SYMBOL_VALUE macro, it is required that the intrinsic is
implemented for every arch that implements AOT.  In this case, there isn't an implementation for x86_64 (yet), so
that's why the failure is occurring.

I was tempted to put in an arch-specific #if for ppc arch only, but I don't see any arch-specific code in this area,
and it doesn't make sense either because AOT isn't supported on ppc at all.  Another alternative is to remove the
SET_AOT_GLOBAL_SYMBOL_VALUE for decodeBlock, since the implementation is not defined (yet) for any arch which supports
AOT.

A third alternative would be to leave the macro call in, but comment it out, saying to uncomment it when it's supported
on all AOT-capable arches.

Any thoughts?

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PR: https://git.openjdk.java.net/jdk/pull/293