谁能告诉我这是什么意思？/usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5.2/../../../crt1.o:Infunction`_start':(.text+0x18):undefinedreferenceto`main'collect2:ldreturned1exitstatusmake:***[program]Error1我的make文件如下所示:program:main.orender.oscreenwriter.og++-omain.orender.oscreenwriter.o-lSDLmain.o:main.cpprender