RFR: CODETOOLS-7903245: Save copy of `make` command after running `make/build.sh`

[Jonathan Gibbons]

Please review a simple change to save a copy of the make command generated by `make/build.sh`, for later reuse to bypass downloading and building dependencies.

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Commit messages:
 - CODETOOLS-7903245: Save copy of `make` command after running `make/build.sh`

Changes: https://git.openjdk.org/jtreg/pull/98/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=98&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903245
  Stats: 22 lines in 1 file changed: 7 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jtreg/pull/98.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/98/head:pull/98

PR: https://git.openjdk.org/jtreg/pull/98