fix manylinux compile error caused by inference lib

[Superjomn]

fixes: #10985

[luotao1]

Maybe you can fix the warning at the same time:

[13:37:36]	[Step 1/1] [ 98%] Building CXX object paddle/contrib/inference/CMakeFiles/test_paddle_inference_api_impl.dir/test_paddle_inference_api_impl.cc.o
[13:37:43]	[Step 1/1] /paddle/paddle/contrib/inference/test_paddle_inference_api_impl.cc: In member function 'virtual void paddle::paddle_inference_api_impl_word2vec_Test::TestBody()':
[13:37:43]	[Step 1/1] /paddle/paddle/contrib/inference/test_paddle_inference_api_impl.cc:75:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
[13:37:43]	[Step 1/1]      for (int j = 0; j < len / sizeof(float); ++j) {
[13:37:43]	[Step 1/1]                        ^
[13:37:43]	[Step 1/1] In file included from /paddle/paddle/contrib/inference/test_paddle_inference_api_impl.cc:16:0:
[13:37:43]	[Step 1/1] /paddle/build/third_party/install/gtest/include/gtest/gtest.h: In instantiation of 'testing::AssertionResult testing::internal::CmpHelperEQ(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = int]':
[13:37:43]	[Step 1/1] /paddle/build/third_party/install/gtest/include/gtest/gtest.h:1421:23:   required from 'static testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = int; bool lhs_is_null_literal = false]'
[13:37:43]	[Step 1/1] /paddle/paddle/contrib/inference/test_paddle_inference_api_impl.cc:71:233:   required from here
[13:37:43]	[Step 1/1] /paddle/build/third_party/install/gtest/include/gtest/gtest.h:1392:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
[13:37:43]	[Step 1/1]    if (lhs == rhs) {
[13:37:43]	[Step 1/1]            ^

https://paddleci.ngrok.io/viewLog.html?buildId=37163&buildTypeId=Paddle_PrCi&tab=buildLog&_focus=7742#_state=72

[luotao1]

There is still warning:

[17:47:04]	[Step 1/1] In file included from /paddle/paddle/contrib/inference/test_paddle_inference_api_impl.cc:16:0:
[17:47:04]	[Step 1/1] /paddle/build/third_party/install/gtest/include/gtest/gtest.h: In instantiation of 'testing::AssertionResult testing::internal::CmpHelperEQ(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = int]':
[17:47:04]	[Step 1/1] /paddle/build/third_party/install/gtest/include/gtest/gtest.h:1421:23:   required from 'static testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = int; bool lhs_is_null_literal = false]'
[17:47:04]	[Step 1/1] /paddle/paddle/contrib/inference/test_paddle_inference_api_impl.cc:71:233:   required from here
[17:47:04]	[Step 1/1] /paddle/build/third_party/install/gtest/include/gtest/gtest.h:1392:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
[17:47:04]	[Step 1/1]    if (lhs == rhs) {
[17:47:04]	[Step 1/1]            ^

https://paddleci.ngrok.io/viewLog.html?buildId=37205&tab=buildLog&buildTypeId=Paddle_PrCi&logTab=tree&filter=all&_focus=7902#_state=75

[luotao1]

LGTM