RFR: 8238320: What is the alignment of padding layouts?

[Maurizio Cimadamore]

Fix padding layout natural alignment so that it is always set to 1 (mininum value). This means that adding a padding layout to a compound layout will be immaterial w.r.t. the group layout's alignment constraint.

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Commits:
 - 60c917cb: Fixed definition of natural alignment for padding layouts. Now padding layout have a natural alignment of 1, which means they do not cause any spurious layout constraint to be inserted into the enclosing struct/union.

Changes: https://git.openjdk.java.net/panama-foreign/pull/8/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/8/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8238320
  Stats: 51 lines in 3 files changed: 40 ins; 9 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/8.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/8/head:pull/8

PR: https://git.openjdk.java.net/panama-foreign/pull/8