Relax assumption about CUDA library path

On mac 64-bit, the library paths is actually at /usr/local/cuda/lib by default. The assumption that it is always at /usr/local/cuda/lib64 has led to build failures, e.g.,
http://ci.tensorflow.org/view/Nightly/job/nightly-matrix-mac-gpu/100/TF_BUILD_IS_OPT=OPT,TF_BUILD_IS_PIP=PIP,TF_BUILD_PYTHON_VERSION=PYTHON2,label=gpu-mac/console
Change: 136653210

tensorflow/tools/ci_build/builds/test_user_ops.sh

@@ -184,11 +184,23 @@ else
       -I "${TF_INC}" -D GOOGLE_CUDA=1 -x cu -Xcompiler -fPIC || \
       die "nvcc compilation of ${OP_KERNEL_CC} FAILED"
 
+  CUDA_LIB_DIR="/usr/local/cuda/lib64"
+  if [[ ! -d "${CUDA_LIB_DIR}" ]]; then
+    CUDA_LIB_DIR="/usr/local/cuda/lib"
+  fi
+  if [[ ! -d "${CUDA_LIB_DIR}" ]]; then
+    die "ERROR: Failed to find CUDA library directory at either of "
+"/usr/local/cuda/lib and /usr/local/cuda/lib64"
+  fi
+
+  echo "Found CUDA library diretory at: ${CUDA_LIB_DIR}"
+  echo ""
+
   # USER_OP_SO=$(basename $(echo "${OP_KERNEL_CC}" | sed -e 's/\.cc/\.so/'))
   USER_OP_SO="add_one.so"
   "${GPP_BIN}" -std=c++11 ${EXTRA_GPP_FLAGS} \
       -shared -o "${USER_OP_SO}" "${OP_KERNEL_CC}" \
-      "${OP_KERNEL_O}" -I "${TF_INC}" -L "/usr/local/cuda/lib64" \
+      "${OP_KERNEL_O}" -I "${TF_INC}" -L "${CUDA_LIB_DIR}" \
       -fPIC -lcudart || \
       die "g++ compilation of ${OP_KERNEL_CC}" FAILED
 fi