some compile warning with MKLDNN related codes, etc

[luotao1]

There are some compile warning with MKLDNN, the full log is https://paddleci.ngrok.io/viewLog.html?buildId=19199&buildTypeId=Paddle_PrCi&tab=buildLog:

1. A warning in jit_avx512_core_i8i8_pooling.cpp uxlfoundation/oneDNN#157

[09:53:57]W:	 [Step 1/1] /paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_common_conv_kernel.cpp: In lambda function:
[09:53:57]W:	 [Step 1/1] /paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_common_conv_kernel.cpp:2666:42: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Wstrict-overflow]
[09:53:57]W:	 [Step 1/1]      auto emit_fma_block = [&](int kh_step) {
[09:53:57]W:	 [Step 1/1]                           

2. Trainer.cpp

[09:55:41]W:	 [Step 1/1] /paddle/paddle/trainer/Trainer.cpp:141:5:   required from here
[09:55:41]W:	 [Step 1/1] /paddle/build/third_party/install/glog/include/glog/logging.h:717:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
[09:55:41]W:	 [Step 1/1]  DEFINE_CHECK_OP_IMPL(Check_EQ, ==)  // Compilation error with CHECK_EQ(NULL, x)?
[09:55:41]W:	 [Step 1/1]                                 ^
[09:55:41]W:	 [Step 1/1] /paddle/build/third_party/install/glog/include/glog/logging.h:148:53: note: in definition of macro 'GOOGLE_PREDICT_TRUE'
[09:55:41]W:	 [Step 1/1]  #define GOOGLE_PREDICT_TRUE(x) (__builtin_expect(!!(x), 1))
[09:55:41]W:	 [Step 1/1]                                                      ^
[09:55:41]W:	 [Step 1/1] /paddle/build/third_party/install/glog/include/glog/logging.h:717:1: note: in expansion of macro 'DEFINE_CHECK_OP_IMPL'
[09:55:41]W:	 [Step 1/1]  DEFINE_CHECK_OP_IMPL(Check_EQ, ==)  // Compilation error with CHECK_EQ(NULL, x)?
[09:55:41]W:	 [Step 1/1]  ^

3. beam_search_op.cc

[09:57:28]W:	 [Step 1/1] /paddle/paddle/operators/beam_search_op.cc: In member function 'bool paddle::operators::BeamSearch::NextItemSet(std::vector<paddle::operators::BeamSearch::Item>*)':
[09:57:28]W:	 [Step 1/1] /paddle/paddle/operators/beam_search_op.cc:142:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
[09:57:28]W:	 [Step 1/1]      for (int d = 0; d < instance_dim; d++) {
[09:57:28]W:	 [Step 1/1]                        ^

4. test_MKLDNN.cpp

[10:13:00]W:	 [Step 1/1] /paddle/paddle/gserver/tests/test_MKLDNN.cpp:318:3:   required from here
[10:13:00]W:	 [Step 1/1] /paddle/build/third_party/install/glog/include/glog/logging.h:721:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
[10:13:00]W:	 [Step 1/1]  DEFINE_CHECK_OP_IMPL(Check_GE, >=)
[10:13:00]W:	 [Step 1/1]                                 ^
[10:13:00]W:	 [Step 1/1] /paddle/build/third_party/install/glog/include/glog/logging.h:148:53: note: in definition of macro 'GOOGLE_PREDICT_TRUE'
[10:13:00]W:	 [Step 1/1]  #define GOOGLE_PREDICT_TRUE(x) (__builtin_expect(!!(x), 1))
[10:13:00]W:	 [Step 1/1]                                                      ^
[10:13:00]W:	 [Step 1/1] /paddle/build/third_party/install/glog/include/glog/logging.h:721:1: note: in expansion of macro 'DEFINE_CHECK_OP_IMPL'
[10:13:00]W:	 [Step 1/1]  DEFINE_CHECK_OP_IMPL(Check_GE, >=)
[10:13:00]W:	 [Step 1/1]  ^