tools/jar tests with -Xcheck:jni: WARNING in native method: JNI call made without checking exceptions when required to from CallLongMethodV

If you run tools/jar tests with -Xcheck:jni, it would yield lots of warnings like:

$ CONF=linux-x86_64-server-fastdebug make images run-test TEST=tools/jar TEST_VM_OPTS="-Xcheck:jni"
...
[2019-10-10 20:48:01,701] Agent[17]: stdout: WARNING in native method: JNI call made without checking exceptions when required to from CallLongMethodV
[2019-10-10 20:48:01,701] Agent[17]: stdout: at com.sun.java.util.jar.pack.NativeUnpack.start(java.base@14-internal/Native Method)
[2019-10-10 20:48:01,701] Agent[17]: stdout: - locked <0x00000000ff3ffa58> (a com.sun.java.util.jar.pack.NativeUnpack)
[2019-10-10 20:48:01,701] Agent[17]: stdout: at com.sun.java.util.jar.pack.NativeUnpack.run(java.base@14-internal/NativeUnpack.java:199)
[2019-10-10 20:48:01,701] Agent[17]: stdout: at com.sun.java.util.jar.pack.NativeUnpack.run(java.base@14-internal/NativeUnpack.java:248)
[2019-10-10 20:48:01,701] Agent[17]: stdout: at com.sun.java.util.jar.pack.UnpackerImpl.unpack(java.base@14-internal/UnpackerImpl.java:115)
[2019-10-10 20:48:01,701] Agent[17]: stdout: - locked <0x00000000ff3fd498> (a com.sun.java.util.jar.pack.UnpackerImpl)
[2019-10-10 20:48:01,701] Agent[17]: stdout: at com.sun.java.util.jar.pack.UnpackerImpl.unpack(java.base@14-internal/UnpackerImpl.java:147)
[2019-10-10 20:48:01,701] Agent[17]: stdout: - locked <0x00000000ff3fd498> (a com.sun.java.util.jar.pack.UnpackerImpl)
[2019-10-10 20:48:01,701] Agent[17]: stdout: at sun.tools.jar.Main.run(jdk.jartool@14-internal/Main.java:343)
[2019-10-10 20:48:01,701] Agent[17]: stdout: - locked <0x00000000ff4deda8> (a sun.tools.jar.Main)
[2019-10-10 20:48:01,702] Agent[17]: stdout: at sun.tools.jar.JarToolProvider.run(jdk.jartool@14-internal/JarToolProvider.java:37)
[2019-10-10 20:48:01,702] Agent[17]: stdout: at DeprecateOptionN.jar(DeprecateOptionN.java:52)
[2019-10-10 20:48:01,702] Agent[17]: stdout: at DeprecateOptionN.normalizeWithWarning(DeprecateOptionN.java:74)
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