RFR: 7903239: ofAddress factory of function pointer type is wrong for struct returns [v4]

[Marko]

> When generating the lambda inside the `ofAddress` factory, it is missing the `SegmentAllocator` needed when the function returns a struct. This is [implemented for regular functions](https://github.com/openjdk/jextract/blob/0582eaf1b4cdba95f0ee8c2480767433bb647d0d/src/main/java/org/openjdk/jextract/impl/HeaderFileBuilder.java#L122-L127), but not for function pointers.

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

  newline

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Changes:
  - all: https://git.openjdk.org/jextract/pull/58/files
  - new: https://git.openjdk.org/jextract/pull/58/files/851d4b33..c23b05b5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=58&range=03
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=58&range=02-03

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/58.diff
  Fetch: git fetch https://git.openjdk.org/jextract pull/58/head:pull/58

PR: https://git.openjdk.org/jextract/pull/58