[code-reflection] Integrated: SPIRV backend needs extra dependencies make it optional

[Gary Frost]

SPIRV requires Tornado spirv lib.  So we will make it optional.

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Commit messages:
 - SPIRV backend needs extra dependencies make it optional

Changes: https://git.openjdk.org/babylon/pull/134/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=134&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/babylon/pull/134.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/134/head:pull/134

PR: https://git.openjdk.org/babylon/pull/134