[foreign-jextract] RFR: 8256247: TestUpcallHighArity fails on AArch64

[Nick Gasson]

Large (> 16 byte) struct arguments should be passed by reference to a
caller-allocated copy of the struct. If this argument is passed on the
stack then the pointer should occupy a single stack slot. However the
current CallArranger allocates enough stack slots to hold the entire
struct, which is incorrect.

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Commit messages:
 - 8256247: TestUpcallHighArity fails on AArch64

Changes: https://git.openjdk.java.net/panama-foreign/pull/392/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=392&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256247
  Stats: 39 lines in 2 files changed: 37 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/392.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/392/head:pull/392

PR: https://git.openjdk.java.net/panama-foreign/pull/392