#ifdef LIB_OPT /* We are building in testLib4libopt. Provide the correct symbol. */ int testLib4libopt(void) { return 0; } #else /* We are not building in testLib4libopt. Poison the symbol. */ extern int testLib4libopt_noexist(void); int testLib4libopt(void) { return testLib4libopt_noexist(); } #endif