[foreign] RFR: 8223808: initial port for AArch64

[Nick Gasson]

Hi all,

I've put an updated webrev for the AArch64 port here:

http://cr.openjdk.java.net/~ngasson/foreign/8223808/webrev.2/

This contains all the previous changes plus a few fixes to handle things
like "heterogeneous float aggregates" (structs/arrays where all the
members are float/double), which are handled specially in the ABI.

With this patch all the tests in the jdk_foreign group pass on AArch64,
except the two I disabled pending adding long double support.

Please let me know if you have any feedback!

Thanks,
Nick