RFR: 8346132: fallbacklinker.cpp failed compilation due to unused variable

[Calvin Cheung]

A simple fix for removing an unused variable in fallbacklinker.cpp. This is needed for building zero jvm variant on macosx-x64.

Testing:

- [x] tier1
- [x] zero jvm variant build on macosx-x64

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Commit messages:
 - 8346132: fallbacklinker.cpp failed compilation due to unused variable

Changes: https://git.openjdk.org/jdk/pull/22799/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22799&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346132
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22799.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22799/head:pull/22799

PR: https://git.openjdk.org/jdk/pull/22799