Fix: cppunit tests broken by squid.h defines

Fix: cppunit tests broken by squid.h defines

In order to promote safe coding and the use of internal accounting API
Squid mangles certain common function definitions such as malloc/calloc.

While this is a great idea for Squid internal code. It's not good when
integrating external cppunit macro libraries. At least one of which in
use performs its own allocation during testing.

This adds an extra layer of protection to prevent redirection with certain
unit-tests where the macros needed clash with Squid.