RFR: 8282883: Use JVM_LEAF to avoid ThreadStateTransition for some simple JVM entries

[Yi Yang]

Some existing JVM_ENTRY routines are behavioral simple, they do not lock, GC or throw exceptions, we could use JVM_LEAF instead of JVM_ENTRY, to avoid ThreadStateTransition and safepoint checks.

-------------

Commit messages:
 - 8282883: Use JVM_LEAF to avoid ThreadStateTransition for some simple JVM entries

Changes: https://git.openjdk.java.net/jdk/pull/7760/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7760&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282883
  Stats: 8 lines in 1 file changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7760.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7760/head:pull/7760

PR: https://git.openjdk.java.net/jdk/pull/7760