RFR (M) 8207359: Make SymbolTable increment_refcount disallow zero

[coleen.phillimore at oracle.com]

Summary: Use cmpxchg for non permanent symbol refcounting, and pack 
refcount and length into an int.

This is a precurser change to the concurrent SymbolTable change. Zeroed 
refcounted entries can be deleted at anytime so they cannot be allowed 
to be zero in runtime code.  Thanks to Kim for writing the packing 
function and helping me avoid undefined behavior.

open webrev at http://cr.openjdk.java.net/~coleenp/8207359.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8207359

Tested with solaris ptrace helper, mach5 tier1-5 including solaris. 
Added multithreaded gtest which exercises the code.

Thanks,
Coleen