CC & CXX env vars are erroneously set for child processes
When doing a cross platform compilation, CMAKE_C_COMPILER & CMAKE_CXX_COMPILER is setup as described in https://cmake.org/cmake/help/v3.6/manual/cmake-toolchains.7.html.
When execute_process(COMMAND env) is run in a CMakeLists.txt file, the output shows that CC & CXX environment variables are set to the values from the toolchain file. This makes it impossible to setup a tool build which uses the default build system.