RFR(XS): 8145543: Removed @ignore for compiler/floatingpoint/ModNaN.java

[Max Ockner]

Hello,
Please review this extra small change. There was supposedly a bug which 
caused compiler/floatingpoint/ModNaN.java to fail, but this bug is not 
reproducible. I have removed the @ignore for this test.

bug: https://bugs.openjdk.java.net/browse/JDK-8145543
webrev: http://cr.openjdk.java.net/~mockner/8145543/

I ran this change through jprt several times and saw no failure. I also 
had clean runs on several other machines, including a Standard Oracle 
Linux linux-x64 JDK9 machine. This issue that caused this bug originally 
(https://sourceware.org/bugzilla/show_bug.cgi?id=14048) has been 
patched, and the patch has been backported to previous versions.  It is 
now very difficult to find a machine which is far enough out of date to 
still have this issue.

Thanks,
Max