When compiling without c++ enabled, some variables are not present.
This is a check enforced in recent Cmake versions.
CMake Error at CMakeModules/AddZstdCompilationFlags.cmake:54 (list):
list sub-command REMOVE_DUPLICATES requires list to be present.
Call Stack (most recent call first):
CMakeLists.txt:53 (ADD_ZSTD_COMPILATION_FLAGS)
The CMAKE_BUILD_TYPE variable is a CACHE variable
and should be set in a way that persists and is
documented in the CACHE. Also set the default
values for the gui to ease selection of types.
These changes provide better support for GUI
configurators that support cmake.
Ancient versions of CMake required else(), endif(), and similar block
termination commands to have arguments matching the command starting the block.
This is no longer the preferred style.
Hans Johnson