RFR: CODETOOLS-7903281: support alternate build for FAQ

[Jonathan Gibbons]

Please review a small update to allow an alternate form of the FAQ to be generated, with different/extra options for `pandoc` and `sed`.

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Commit messages:
 - CODETOOLS-7903281: support alternate build for FAQ

Changes: https://git.openjdk.org/jtreg/pull/110/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=110&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903281
  Stats: 11 lines in 2 files changed: 8 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jtreg/pull/110.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/110/head:pull/110

PR: https://git.openjdk.org/jtreg/pull/110