[CMake] CMake 3.15 fails to install on OS X

[Jeffrey Walton]

I'm building CMake cmake-3.15.4.tar.gz on OS X 10.12. The machine is
stripped down, and only has the COmmand Line tools. No Xcode and
friends.

I configured with:

    ./configure --prefix=/usr

Configure appears OK. Make appears OK. Install is failing:

    $ sudo make install VERBOSE=1
    ...
[100%] Built target foo
/Users/jwalton/cmake-3.15.4/Bootstrap.cmk/cmake -E
cmake_progress_start /Users/jwalton/cmake-3.15.4/CMakeFiles 0
/Library/Developer/CommandLineTools/usr/bin/make -f
CMakeFiles/Makefile2 preinstall
make[1]: Nothing to be done for `preinstall'.
Install the project...
bin/cmake -P cmake_install.cmake
-- Install configuration: ""
CMake Error at Source/kwsys/cmake_install.cmake:36 (file):
  file cannot create directory: /usr/doc/cmake-3.15/cmsys.  Maybe need
  administrative privileges.
Call Stack (most recent call first):
  cmake_install.cmake:37 (include)

make: *** [install] Error 1