[foreign-abi] RFR: 8241712: AArch64: TestDowncall fails with IllegalArgumentException: No ABI attribute present

[Nick Gasson]

Tests cases where the structure has an initial floating point element followed by padding fail with this exception. The
padding element doesn't have the NATIVE_TYPE attribute.

  test TestDowncall.testDowncall("f0_V_S_FD", VOID, [STRUCT], [FLOAT, DOUBLE]): failure
  java.lang.IllegalArgumentException: No ABI attribute present
          at jdk.incubator.foreign/jdk.incubator.foreign.SystemABI$Type.lambda$fromLayout$0(SystemABI.java:195)
          at java.base/java.util.Optional.orElseThrow(Optional.java:401)
          at jdk.incubator.foreign/jdk.incubator.foreign.SystemABI$Type.fromLayout(SystemABI.java:195)
          at
          jdk.incubator.foreign/jdk.internal.foreign.abi.aarch64.CallArranger.isHomogeneousFloatAggregate(CallArranger.java:207)
          at jdk.incubator.foreign/jdk.internal.foreign.abi.aarch64.CallArranger.classifyStructType(CallArranger.java:220)

-------------

Commit messages:
 - 8241712: AArch64: TestDowncall fails with IllegalArgumentException: No ABI attribute present

Changes: https://git.openjdk.java.net/panama-foreign/pull/70/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/70/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8241712
  Stats: 14 lines in 2 files changed: 12 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/70.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/70/head:pull/70

PR: https://git.openjdk.java.net/panama-foreign/pull/70