RFR: 8223188: Consider rewriting in C++ or moving to ".c" files

[Alexey Semenyuk]

Remove needless `#ifdef __cplusplus` from .cpp sources

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Commit messages:
 - 8223188: Consider rewriting in C++ or moving to ".c" files

Changes: https://git.openjdk.java.net/jdk/pull/2466/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2466&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8223188
  Stats: 10 lines in 2 files changed: 0 ins; 6 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2466.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2466/head:pull/2466

PR: https://git.openjdk.java.net/jdk/pull/2466