[CMake] Is it possible to patch a make project with CMakeLists.txt, through external_project_add?

[mike lojkovic]

So, I'm trying to get my project to work on Windows, as well as Linux.
Currently, everything compiles fine on Linux. I've gotten it to
compile in the past on Windows, but since then have reinstalled
Windows, and forgotten the precise steps needed to manually setup Lua,
so CMake can find it. So, I assume just add Lua to my project with
ExternalProject_Add, but they use make and the makefil is configured
for Linux.

The two options I have are either patch their makefile to build
correctly through cygwin, (I'm just worried this might lead to issues
with producing a binary requiring cygwin) or add a CMakeLists.txt file
and patch it in after the download ends. How would I go about adding
custom CMakeLists.txt file to their project after the download
finishes?