RFR: 8344989: Test java/foreign/TestLinker.java failed with zero: IllegalStateException: libffi call failed with status: FFI_BAD_TYPEDEF

[Per Minborg]

This PR proposes to check for empty layouts in the fallback linker and then prevent them from being forwarded.

Passes tier5 linker tests.

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Commit messages:
 - Fix fallback linker issues

Changes: https://git.openjdk.org/jdk/pull/22417/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22417&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344989
  Stats: 43 lines in 2 files changed: 41 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22417.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22417/head:pull/22417

PR: https://git.openjdk.org/jdk/pull/22417