In find-package mode, cmake executes Modules/CMakeFindPackage.cmake,
which calls find_package(), and this is then evaluated in cmake.cxx,
which prints an appropriate message to stdout, so it can be used
e.g. in a normal Makefile:

$ /opt/cmake-HEAD/bin/cmake --find-package -DNAME=JPEG
 -DCOMPILER_ID=GNU -DLANGUAGE=C -DMODE=EXIST
JPEG found.
$ /opt/cmake-HEAD/bin/cmake --find-package -DNAME=JPEG
 -DCOMPILER_ID=GNU -DLANGUAGE=C -DMODE=COMPILE

$ /opt/cmake-HEAD/bin/cmake --find-package -DNAME=JPEG
 -DCOMPILER_ID=GNU -DLANGUAGE=C -DMODE=LINK
-rdynamic -ljpeg

Alex