test/suites/api: Detect tests correctly
test/suites/api: Detect tests correctly

The C++ test case didn't work correctly in VPATH builds or with
VALGRIND=1.

yahoo/ygloo-external-jansson,akheron/jansson,janetuk/jansson,Mephistophiles/jansson,AmesianX/jansson,janetuk/jansson,gameclosure/jansson,gameclosure/jansson,wirebirdlabs/featherweight-jansson,firepick1/jansson,rogerz/jansson,akheron/jansson-debian,firepick1/FireSight,gameclosure/jansson,npmccallum/jansson,akheron/jansson-debian,slackner/jansson,firepick1/FireSight,janetuk/jansson,liu3tao/jansson,rogerz/jansson,markalanj/jansson,janetuk/jansson,firepick-delta/FireSight,liu3tao/jansson,bstarynk/jansson,akheron/jansson-debian,firepick1/jansson,simonfojtu/FireSight,bstarynk/jansson,chrullrich/jansson,yahoo/ygloo-external-jansson,akheron/jansson,firepick1/jansson,yahoo/ygloo-external-jansson,Vorne/jansson,firepick1/FireSight,wirebirdlabs/featherweight-jansson,simonfojtu/FireSight,OlehKulykov/jansson,OlehKulykov/jansson,bstarynk/jansson,AmesianX/jansson,markalanj/jansson,slackner/jansson,yahoo/ygloo-external-jansson,npmccallum/jansson,Vorne/jansson,akheron/jansson,chrullrich/jansson,attie/jansson,Mephistophiles/jansson,akheron/jansson-debian,attie/jansson,firepick-delta/FireSight,simonfojtu/FireSight,rogerz/jansson,firepick-delta/FireSight,markalanj/jansson,rogerz/jansson