cmake HAVE_COHERENT_DMA examples

linux-rdma/rdma-core CMakeLists.txt :541

CHECK_C_SOURCE_COMPILES("
#if !defined(__s390x__)
#include \"${CMAKE_CURRENT_SOURCE_DIR}/util/udma_barrier.h\"
#endif
 int main(int argc,const char *argv[]) {return 0;}"
  HAVE_COHERENT_DMA)