Combine all the lines of a text file into a single line via the Windows Command line

I ended up finding the answer in another question, here in Stack Overflow

@ECHO OFF
setlocal
(SET file-list=)
FOR /f "delims=" %%x IN (7z-Compression-List.txt) DO (
CALL SET file-list=%%file-list%%, %%x
)
SET file-list=%file-list:~1%
ECHO file-list=%file-list%

It worked beautifully. This is a modified copy of Magoo's answer, so feel free to upvote original author if you like this answer.