RFR: 7903982: JMH: Fallback xctrace profiler resolution on SDKROOT env variable

[Galder Zamarreño]

If `xctrace` cannot be found via `xcode-select` it checks the SDKROOT environment variable.

@fzhinkin Can you have a look?

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Commit messages:
 - 7903982: JMH: Fallback xctrace resolution on SDKROOT

Changes: https://git.openjdk.org/jmh/pull/155/files
  Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=155&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903982
  Stats: 24 lines in 1 file changed: 18 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jmh/pull/155.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/155/head:pull/155

PR: https://git.openjdk.org/jmh/pull/155