[jenkins] - add gtest buildstep for jenkins (osx32, osx64m linux32, linu...

...x64).

I missed to PR those scripts when i did the gtest jenkins integration. Those scripts are called by jenkins when the checkbox "RUN_TESTS" is marked on the jenkins job. Those don't influence the normal compile approach or something - but make gtest integration in jenkins work (tests are turned off by default though because they are not passed on all platforms yet iirc ;) ).

Also that way we are able to test compilation of osx using make instead of xcode (cause 99% of xbmc's code is compiled and linked to the gtest binary and this is done via make on osx like on the other platforms)...

There is no script for windows yet - but wsoltys knows about it ...