ORC-265: [C++] Add documentation for C++ build support

[majetideepak]

I verified the modified page by building locally.

[owen-hortonworks]

I'd suggest using:

cmake .. -DSNAPPY_HOME=<PATH> -DZLIB_HOME=<PATH> ...

to be more consistent.

[majetideepak]

Hi Owen, the current setup depends on <LIBNAME>_HOME being environmental variables and not CMake variables.

[wgtmac]

I need to explicitly set OPENSSL_ROOT_DIR on my mac, otherwise I will end up with the following error message:

CMake Error at /Applications/CMake.app/Contents/share/cmake-3.7/Modules/FindPackageHandleStandardArgs.cmake:138 (message):
Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the
system variable OPENSSL_ROOT_DIR (missing: OPENSSL_INCLUDE_DIR)
Call Stack (most recent call first):
/Applications/CMake.app/Contents/share/cmake-3.7/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
/Applications/CMake.app/Contents/share/cmake-3.7/Modules/FindOpenSSL.cmake:385 (find_package_handle_standard_args)
CMakeLists.txt:41 (find_package)

[majetideepak]

@wgtmac That is correct. We manually set it in travis-ci testing as well.
cmake -DOPENSSL_ROOT_DIR=`brew --prefix openssl` ..
I will check with Anatoli Shein if we can fix this / or add documentation here. Thanks!

[owen-hortonworks]

I'm using cmake 3.5.1, but it works for me. Why would you need environment variables instead of cmake variables?

[owen-hortonworks]

Actually, looking at the ThirdpartyToolchain.cmake, it goes the other way. It is looking at the environment variable and setting the cmake variable. Setting the cmake variable directly works fine.

[majetideepak]

That is correct. The recent changes made did put the dependency on CMake variables. Fixed the doc.