WinFlex and WinBison are required to compile ZC with ZScript support.
Before you run CMake, you should install them using this exe file, 
and set the path for them!

My own wandering through the woods, twice now, setting up
Flex/Bison for ZC was a pain in the arse. Here are my path values;
and I also had to manually add it in a shell. Go figure. 

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User Path
C:\flex;C:\Program Files\CMake\bin

System Path
C:\flex\;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Program Files\Dell\DW WLAN Card;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\;C:\Program Files\Git\cmd;C:\Program Files (x86)\Microsoft SQL Server\90\Tools\binn\;C:\Program Files (x86)\WinMerge;C:\Program Files (x86)\Skype\Phone\

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//Manual Path Config from CMD.com

set PATH=%PATH%;C:\flex

in the command window you have open.

Breaking it down:

set PATH=%PATH%;  -- takes the current path and sets PATH to it.
C:\flex      -- Adds this directory to the path, because of 'set PATH' this is added

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Once you do all of this, CMake should be able to detect flex-bison. 

-Z