CMakeLists.txt: add LOG4CPLUS_BUILD_TESTING switch
CMakeLists.txt: add LOG4CPLUS_BUILD_TESTING switch

This new switch make it possible to omit the tests.

ccpaging/log4cplus,csuideal/log4cplus,ccpaging/log4cplus,ccpaging/log4cplus,ccpaging/log4cplus,csuideal/log4cplus,hunter-packages/log4cplus,csuideal/log4cplus,hunter-packages/log4cplus,csuideal/log4cplus,hunter-packages/log4cplus,hunter-packages/log4cplus