Fix the linking error for iOS simulator (architecture x86_64). (#6081)

paddle/math/CMakeLists.txt

@@ -26,8 +26,6 @@ else()
 endif()
 
 if(MOBILE_INFERENCE)
-    list(REMOVE_ITEM MATH_SOURCES
-         ${CMAKE_CURRENT_SOURCE_DIR}/SIMDFunctions.cpp)
     # Remove sparse
     list(REMOVE_ITEM MATH_HEADERS
          ${CMAKE_CURRENT_SOURCE_DIR}/CpuSparseMatrix.h

paddle/math/SIMDFunctions.h

@@ -116,9 +116,11 @@ inline bool vec_check(size_t len) {
 }
 
 namespace internal {
+#ifdef __SSE3__
 void addToImpl(float* a, const float* b, size_t len);
 void batchAddToImpl(float* a, const float* b[], int batch, size_t len);
 void colMaxImpl(float* result, const float* data, int dim, int numSamples);
+#endif
 #ifdef __AVX__
 void decayL1AvxImpl(float* dst, float* src, float lambda, size_t len);
 void decayL1AvxImpl(