I just did a clean install of Mac OS X 10.8 Mountain Lion and Xcode 4.4 so when I was ready to compile (again…) OpenCV 2.4.2 I got this error executing “cmake ..”:

$ cmake ..
CMake Error: CMake was unable to find a build program corresponding to "Unix Makefiles".  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_CXX_COMPILER_ENV_VAR
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_CXX_COMPILER
CMake Error: Could not find cmake module file:/Users/enekochan/compilaciones/OpenCV-2.4.2/build/CMakeFiles/CMakeCXXCompiler.cmake
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_C_COMPILER_ENV_VAR
CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.
Missing variable is:
CMAKE_C_COMPILER
CMake Error: Could not find cmake module file:/Users/enekochan/compilaciones/OpenCV-2.4.2/build/CMakeFiles/CMakeCCompiler.cmake
CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage
CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage
-- Configuring incomplete, errors occurred!

New versions of Xcode (4.4 and above) don’t install themselves in /Developer so I thought it could be a path issue, but the real problem is that the terminal utilities are not included in the normal install of Xcode anymore and you have to download them separately from https://developer.apple.com/downloads/ (you need an Apple ID). Then look for the latest “Command Line Tools” for your system:

Install it and you will be able to compile from the terminal.

Source: http://www.cmake.org/pipermail/cmake/2009-February/027317.html