[FIX] Build process shouldn’t modify source tree

[codingforfun]

It’s best practice to not modify the source tree during build time.
CMake strongly encourages this.
This PR changes the cmake build process to create the confuigured header file build_config.h in the build tree instead of the source tree.

[codingforfun]

Travis fails on some utests build using Makefiles separate from the ones build by CMake.
Is that really used anymore. Test build with CMake work. I’m not very keen to dive into some ancient stuff if it’s not needed any more.

[hcho3]

@codingforfun See #561. This is an issue unrelated to your work here, so don't worry about it.

[hcho3]

LGTM

[rongou]

This seems to break the xgboost build:

git clone --recurse-submodules https://github.com/dmlc/xgboost.git
cd xgboost
mkdir build
cd build
cmake ..
make

I get the following error:

In file included from /home/rou/src/xgboost/include/../../dmlc-core/include/dmlc/./logging.h:16,
                 from /home/rou/src/xgboost/include/../../dmlc-core/include/dmlc/io.h:15,
                 from /home/rou/src/xgboost/rabit/include/rabit/./internal/../serializable.h:14,
                 from /home/rou/src/xgboost/rabit/include/rabit/./internal/engine.h:10,
                 from /home/rou/src/xgboost/rabit/include/rabit/rabit.h:48,
                 from /home/rou/src/xgboost/src/common/timer.cc:4:
/home/rou/src/xgboost/include/../../dmlc-core/include/dmlc/././base.h:282:10: fatal error: dmlc/build_config.h: No such file or directory
 #include <dmlc/build_config.h>
          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.
src/CMakeFiles/objxgboost.dir/build.make:153: recipe for target 'src/CMakeFiles/objxgboost.dir/common/timer.cc.o' failed
make[2]: *** [src/CMakeFiles/objxgboost.dir/common/timer.cc.o] Error 1
CMakeFiles/Makefile2:295: recipe for target 'src/CMakeFiles/objxgboost.dir/all' failed
make[1]: *** [src/CMakeFiles/objxgboost.dir/all] Error 2
Makefile:129: recipe for target 'all' failed
make: *** [all] Error 2

Any ideas on what's going on?

[hcho3]

@rongou I just tried git clone --recurse-submodules https://github.com/dmlc/xgboost.git and I cannot reproduce the problem.

[rongou]

Hmm never mind. Somehow it's picking up a separate dmlc-core repo on my drive. Once I deleted it the problem went away.