how to get all the prerequisites for building darktable on macOS?
I simply ran your script, and carefully read cmake’s errors and warnings. I then used Homebrew to install stuff that cmake said it couldn’t find.
I was pleasantly surprised to find that /usr/bin/apt exists on MacOS. Then I read the man page, and discovered it’s an “annotation processing tool,” not a package manager. 
I did locate libcurl.dylib and found a number of applications (including the Topaz suite) that included libcurl.dylib in their installation package. otool -L does not note any version number for them, but they are bigger and newer than the /usr/lib/libcurl.dylib that cmake complains about.
I copied one of those libcurl.dylib files into ~/lib, and put that at the head of $LD_LIBRARY_PATH and re-ran cmake, but it did not change the complaint about /usr/lib/libcurl.dylib. It appears cmake is ignoring $LD_LIBRARY_PATH?
I’m not sure what to do at this point.