Make verifiable a DSO and add NAME_SUFFIX support

Build option DSO=1 generates libverifiable.so which can be
used to reduce the combined binary size.

Build option NAME_SUFFIX can be used to a add suffix to all
generated binaries. e.g. NAME_SUFFIX=_mpi

Added new make target: clean_intermediates

verifiable/main.cu

@@ -0,0 +1,14 @@
+
+#include <cuda_runtime.h>
+#include <iostream>
+
+#define NCCL_VERIFIABLE_SELF_TEST 1
+#include "verifiable.h"
+
+int main(int arg_n, char **args) {
+  std::cerr<<"You are hoping to see no output beyond this line."<<std::endl;
+  cudaSetDevice(0);
+  ncclVerifiableLaunchSelfTest();
+  cudaDeviceSynchronize();
+  return 0;
+}