The recommended way to change compilers is by using the CC and CXX environment variable, which CMake respects.
$ export CC=/usr/bin/clang
$ export CXX=/usr/bin/clang++
$ cmake ..
-- The C compiler identification is Clang
-- The CXX compiler identification is Clang
http://stackoverflow.com/a/7032021/2297501
Everyone has edit access to the wiki (however -DCMAKE_C_COMPILER shouldn't be there).