[foreign-memaccess+abi] RFR: 8292078: Thread-safety issues in AbstractLinker implementations [v5]

[Per Minborg]

On Tue, 9 Aug 2022 13:13:41 GMT, Per Minborg <duke at openjdk.org> wrote:

>> Change to lazy static initializing for singletons and fix a bug in `LinuxAArch64VaList` that threw an `IndexOutOfBoundsException`.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use local class holders

src/java.base/share/classes/jdk/internal/foreign/abi/aarch64/linux/LinuxAArch64Linker.java line 45:

> 43: public final class LinuxAArch64Linker extends AbstractLinker {
> 44: 
> 45:     public static LinuxAArch64Linker getInstance() {

I think the `getInstance()` method should only return `Linker`.

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PR: https://git.openjdk.org/panama-foreign/pull/702