RFR: 8274550: c2i entry barriers read int as long on PPC

[Martin Doerr]

`_keep_alive` is an int. We shouldn't use a 64 bit load.

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Commit messages:
 - 8274550: c2i entry barriers read int as long on PPC

Changes: https://git.openjdk.java.net/jdk/pull/5776/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5776&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274550
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5776.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5776/head:pull/5776

PR: https://git.openjdk.java.net/jdk/pull/5776