example: Add missing stdlib.h.
example: Add missing stdlib.h.

This fixes a build error on Windows.

jschmidlapp/cmocka,jschmidlapp/cmocka,chadversary/cmocka,jamesmunns/CMocka,aleksandr-vin/cmock,lsjostro/cmocka,chadversary/cmocka,nuumio/cmocka,wingyplus/cmocka,wingyplus/cmocka,jhrozek/cmocka,nuumio/cmocka,jhrozek/cmocka,aleksandr-vin/cmock,Odie/cmocka,dsch/cmocka,clibs/cmocka,tyc/cmocka,jhrozek/cmocka,jamesmunns/CMocka,tyc/cmocka,JonathonReinhart/cmocka,jschmidlapp/cmocka,clibs/cmocka,dsch/cmocka,lsjostro/cmocka,Odie/cmocka,Odie/cmocka,tyc/cmocka,VladimirTyrin/cmocka,nuumio/cmocka,linuxmaniac/cmocka,VladimirTyrin/cmocka,linuxmaniac/cmocka,JonathonReinhart/cmocka