Should not compile the two files if -DWITH_AVX=OFF. (#163)

* If cmake -DWITH_AVX=OFF during configuration, should not compile the file src/hl_math.cc and src/hl_avx_functions.cc.

paddle/cuda/CMakeLists.txt

@@ -2,10 +2,17 @@ set(AVX_SOURCES
     src/hl_math.cc
     src/hl_avx_functions.cc
 )
-set(CUDA_SOURCES
+
+if(WITH_AVX)
+    set(CUDA_SOURCES
         src/hl_time.cc
         src/hl_cpu_functions.cc
         ${AVX_SOURCES})
+else()
+    set(CUDA_SOURCES
+        src/hl_time.cc
+        src/hl_cpu_functions.cc)
+endif()
 
 set(CUDA_CXX_WITH_GPU_SOURCES
     src/hl_cuda_cublas.cc