CMake comes in two forms - command line and gui. Some installations only install one or the other, but sometimes both. The build commands below are only for the command line use.
Also the actual build tools vary for each platform. But that is one of the great features of cmake, it can generate variuous 'native' build files. Running cmake without any parameters will list the generators available on that platform. For sure one of the common ones is "Unix Makefiles", which needs autotools make installed, but many other generators are supported.
In windows cmake offers various versions of MSVC. Again below only the command line use of MSVC is shown, but the tidy solution (*.sln) file can be loaded into the MSVC IDE, and the building done in there.
By default cmake sets the install path to /usr/local in unix. If you wanted the binary in say /usr/bin instead, then in 2. above use -DCMAKE_INSTALL_PREFIX=/usr
Also, in unix if you want to build the release library without any debug `assert` in the code then add `-DCMAKE_BUILD_TYPE=Release` in step 2. This adds a `-DNDEBUG` macro to the compile switches. This is normally added in windows build for the `Release` config.
In windows the default install is to C:\Program Files\tidy5, or C:/Program Files (x86)/tidy5, which is not very useful. After the build the tidy[n].exe is in the Release directory, and can be copied to any directory in your PATH environment variable, for global use.
If you do **not** need the tidy library built as a 'shared' (DLL) library, then in 2. add the command -DBUILD_SHARED_LIB:BOOL=OFF. This option is ON by default. The static library is always built and linked with the command line tool for convenience in windows, and so the binary can be run as part of the man page build without the shared library being installed in unix.
