add cp27-cp27m-gcc82 and cp27-cp27mu-gcc82 branch to support gcc8.2 compile for paddle, test=develop (#22504)

* polish grad op check, test=develop, test=document_fix

* keep op_use_default_grad_maker.spec to avoid conflict, test=develop, test=document_fix

Add coverage data processing tools.

* add shell scripts. test=develop

* rename test_pybind_inference to test_pybind_interface and print repeat process in check_op_desc.py. test=develop

* add approval RD. test=develop

* add data_type register CI test=develop

* add op add test case test=develop

* add test case for register op kernel test=develop

* fix shell script bug test=develop

* fix checkout branch test=develop

* remove test case code test=develop

* fix op_type.spec name test=develop

* fix default grad op maker ci bug, test=develop, test=document_fix

* remove some ops from paddle/fluid/op_use_default_grad_op_maker.spec, test=develop, test=document_fix

* add unused input vars check for OpWithKernel, test=develop

* remove unused vars in some ops, test=develop

* fix batch_norm, test=develop

* add white list, test=develop

* add CI check for white list, test=develop

* :ove white list to c++, test=develop

* solve failure of CI, test=develop

* add unittest for unused_var_check, test=develop

* refine code, enable check in operator_test, test=develop

* skip mkldnn, test=develop

* extend white list, test=develop

* refine condition of mkldnn, test=develop

* fix paddle_build, test=develop

* follow comments, test=develop

* fix GetExpectedKernelType

* add wiki ref to err_msg, test=develop

* follow comment, test=develop

* add ending message

Add ending message to indicate script execution properly finished

* Update paddle_build.sh

test=develop

* Update paddle_build.sh

test=document_fix

* Update paddle_build.sh

test=develop test=document_fix

* split api_spec document;test=document_fix

* change tools

* test=develop;test=document_fix

* test=develop;test=document_fix

* test=develop

* mv sampcd_processor.py to tools

test=develop test=document_fix

* update example script

test=develop test=document_fix

test=develop

* refine API.spec, test=develop

* add nn.py to test,test=develop

* fix by removing new.spec, test=develop, test=document_fix

* refine scripts when PYTHON_ABI is empty, follow partial comments, add extra cpp api doc, test=develop, test=document_fix

* remove extra doc changes, remove API.spec, test=develop

This PR fix the tag error in paddle_build.sh

* refine print_signatures.py to remove ComposeNotAligned, test=develop

* remove experimental_namespace, test=develop

* add train demo to paddle_build.sh

test=develop
test=document_preview

* code cleaning

* test=develop

test=develop

* remove program desc files

test=develop

* add test_train to CI

test=develop
test=document_preview

* make run.sh excutable

test=develop
test=document_preview

* switch with_mkl to off

test=develop
test=document_preview

* switch with_mkl to off

test=develop

* switch with_mkl to on

test=develop

* move test_fluid_lib_train to ci_py35

test=develop

* fix bugs of MKLDNN building

* rm build_train_lib(), test=develop

* restore tensor.h, test=develop

* change approve site ;test=develop

* test=develop

* modify paddle_build.sh for Paddle python3 version image generation, test=develop

* modify paddle_build.sh for Paddle python3 image generation, test=develop

* add exception exit on error example codes test=develop

test=develop

* change grad_op approval

* test=develop

* CI Add Reviewer Rules

* CI Add Reviewer Rules

* change git_files

* change git_files

* test=develop

* test=develop