RFR: 8345626: Build fails with fatal error: DEBUG_CFLAGS_JDK: No such file or directory

[David Holmes]

Added missing $ to variable expansion.

Local build worked.

Thanks

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Commit messages:
 - 8345626: Build fails with fatal error: DEBUG_CFLAGS_JDK: No such file or directory

Changes: https://git.openjdk.org/jdk/pull/22589/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22589&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345626
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22589.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22589/head:pull/22589

PR: https://git.openjdk.org/jdk/pull/22589