RFR: CODETOOLS-7903661: Defer evaluation of MAKE_ARGS in `make/build.sh`

[Jonathan Gibbons]

Please review a simple script change to allow MAKE_ARGS to be re-specified when invoking the `build/make.sh` file generated when running `make/build.sh`. (Invoking `build/make.sh` directly is a convenient way to bypass downloading and building the dependencies any time you want to build and test `jtreg` itself.)

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Commit messages:
 - CODETOOLS-7903661: Defer evaluation of MAKE_ARGS in `make/build.sh`

Changes: https://git.openjdk.org/jtreg/pull/183/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=183&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903661
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jtreg/pull/183.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/183/head:pull/183

PR: https://git.openjdk.org/jtreg/pull/183