* Add a function to update FLAGS

test=develop

* Add a function to update FLAGS

test=develop

* expr flags

* Add a function to update FLAGS

test=develop

* distinguish public/private vars, test=develop

* fix windows issues, test=develop

* expr flag

* Add functions to get and set FLAGS

test=develop

* Add functions to get and set FLAGS

test=develop

* Add functions to get and set FLAGS

test=develop

* Add functions to get and set flags

test=develop

* Add functions to get and set FLAGS

test=develop

* Add a function to update FLAGS

test=develop

* Add a function to update FLAGS

test=develop

* Add functions to get and set flags in Paddle

test=develop
Co-authored-by: Nsneaxiy <sneaxiy@126.com>

* distinguish public/private vars, test=develop

* fix windows issues, test=develop

* add double grad implementation for dygraph, test=develop

* polish code, add uts, test=develop

* fix place bug, test=develop

* polish codes, add more uts for coverages, test=develop

* add no_grad_set, test=develop

* add star gan ut, test=develop

* follow comments, test=develop

* add recorded cuda memory apis, fix typo, test=develop

* add more ut, test=develop

* follow comments, test=develop

* fix py35 incompatible issues, test=develop

* update ScopeBufferedSSAGraphExecutor&AsyncSSAGraphExecutor&ThreadedSSAGraphExecutor&FastThreadedSSAGraphExecutor&ParallelSSAGraphExecutor&ParallelExecutor for fetching unmerged results.

* add the unit test for fetch_unmerged.

* update ut for multi-card and multi-cpu.

* add the error message and the user suggestion in FetchOpHandle. test=develop

* add some debug flags to auto growth allocator, test=develop

* add comments about auto growth, test=develop

* use system allocator in unittests, test=develop

* fix op bugs, test=develop

* fix tensor copy bug when src and dst are the same, test=develop

* add global value getter setter, test=develop

* fix error messages, test=develop