RFR(S): Dtrace fixes for OS X

[Staffan Larsen]

Hi,

This change fixes a number of smaller issues with DTrace on OS X. The fixes are all in OS X code or in USDT2 code which is only used by OS X, so the impact on Solaris should be zero. I have bundled the fixes for all the bugs together in one review because that was how I developed them. If necessary I’ll split them up before pushing them.

Thanks,
/Staffan

bugs:
  https://bugs.openjdk.java.net/browse/JDK-8029726
  https://bugs.openjdk.java.net/browse/JDK-8029727
  https://bugs.openjdk.java.net/browse/JDK-8029728

webrev: http://cr.openjdk.java.net/~sla/8029726/webrev.00/