[foreign-memaccess+abi] RFR: 8275584: Incorrect stack spilling in CallArranger on MacOS/AArch64 [v3]

[Nick Gasson]

> This patch adds special handling for argument spilling on M1 Mac which does not follow the standard AArch64.  In the standard ABI arguments are first extended to the full 64-bit register width and then spilled but on macOS the arguments are spilled according to their original width and packed using theior natural.  @JornVernee  did most of the work to support this but there were a few issues remaining related to structspilling which I've fixed up in the last commit here.

Nick Gasson has updated the pull request incrementally with one additional commit since the last revision:

  Refactor stackAlloc

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/746/files
  - new: https://git.openjdk.org/panama-foreign/pull/746/files/8af03ba1..d6b97f4b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=746&range=02
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=746&range=01-02

  Stats: 13 lines in 1 file changed: 3 ins; 4 del; 6 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/746.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/746/head:pull/746

PR: https://git.openjdk.org/panama-foreign/pull/746