RFR: Fixed compilation error of libTestHeapDump.c on Windows with VS2010

[Zhengyu Gu]

This patch fixes compilation error reported by Michal Vala [1].

VS2010 compiling C files uses C89 standard, which requires all local 
variables are declared at the beginning of code blocks.


Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/vs2010_c2275/webrev.00/


[1] 
https://post-office.corp.redhat.com/mailman/private/java-team/2017-December/msg00164.html

Thanks,

-Zhengyu