RFR: 8314949: linux PPC64 Big Endian: Implementation of Foreign Function & Memory API

[Martin Doerr]

I've found a way to solve the remaining FFI problem on linux PPC64 Big Endian. Large structs (>8 Bytes) which are passed in registers or on stack require shifting the Bytes in the last slot if the size is not a multiple of 8. This PR adds the required functionality to the Java code.

Please review and provide feedback. There may be better ways to implement it. I just found one which works and makes the tests pass:

Test summary
==============================
   TEST                                              TOTAL  PASS  FAIL ERROR   
   jtreg:test/jdk/java/foreign                          88    88     0     0   


Note: This PR should be considered as preparation work for AIX which also uses ABIv1.

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Commit messages:
 - 8314949: linux PPC64 Big Endian: Implementation of Foreign Function & Memory API

Changes: https://git.openjdk.org/jdk/pull/15417/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15417&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314949
  Stats: 235 lines in 10 files changed: 225 ins; 5 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/15417.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15417/head:pull/15417

PR: https://git.openjdk.org/jdk/pull/15417