Keep a pure usage of generic.cmake

[wangkuiyi]

I notice new hacks in our CMakeLists.txt like the following

Paddle/paddle/fluid/operators/detail/CMakeLists.txt

Lines 4 to 5 in 3ceff30

	set(DISTRIBUTE_COMPILE_FLAGS "-Wno-non-virtual-dtor -Wno-error=non-virtual-dtor -Wno-error=delete-non-virtual-dtor")
	set_source_files_properties(serde_test.cc grpc_server_test.cc PROPERTIES COMPILE_FLAGS ${DISTRIBUTE_COMPILE_FLAGS})

Please remove such hack and never use them. Please make sure that CMakeLists.txt includes only calls to CMake functions defined in generic.cmake.

We used to suffer from the problem that CMake provides a very flexible language and we hack our CMakeLists.txt everywhere. This made it extremely challenging to keep our build process understandable, and it took a huge effort of the team, particular thanks to @gangliao , to clean everything up by developing generic.cmake.

[typhoonzero]

Because grpc implementation and generated code have non-virtual destructors, and the default functions see this as an error. We have to put this hack code in CMakeLists.txt to let distributed library compiles. Will consider a better way to do this. @wangkuiyi