Use find_program() to set CMAKE_C_COMPILER and CMAKE_CXX_COMPILER.
Originally the variables was set to compiler name, without absolute path.
CMake 3.0 tries to find them in CMAKE_FIND_ROOT_PATH (since
CMAKE_FIND_ROOT_PATH_MODE_PROGRAM was set to ONLY) and fails.
- exclude system paths from library search paths
- remove hardcoded paths to compiler
- enable compiling with 3d-parties
- enable build as shared libraries