Xcode 12 - build fails while trying to build kext

Background Information

I'm trying to compile an open-source Xcode project found here:https://github.com/mattingalls/Soundflower

I'm using Xcode version 12. I just opened the existing project file and changed a few of the compiler options. (selected gnu 14 and set the standard library to libc(LLVM C Standard Library with C 11 support))

Problem / Error Message

When I try to build the project, this is the error message I'm getting:

Code Block 
CpResource /Users/admin/Library/Developer/Xcode/DerivedData/Soundflower-dlboyjvoqqpljsbphfsdtbsgcuzd/Build/Products/Debug/Soundflower.kext /Users/admin/Documents/src/Soundflower/Build/InstallerRoot/Library/Extensions/Soundflower.kext/Contents/Resources/Soundflower.kext (in target 'Soundflower' from project 'Soundflower')
    cd /Users/admin/Documents/src/Soundflower/Source
    builtin-copy -exclude .DS_Store -exclude CVS -exclude .svn -exclude .git -exclude .hg -resolve-src-symlinks /Users/admin/Library/Developer/Xcode/DerivedData/Soundflower-dlboyjvoqqpljsbphfsdtbsgcuzd/Build/Products/Debug/Soundflower.kext /Users/admin/Documents/src/Soundflower/Build/InstallerRoot/Library/Extensions/Soundflower.kext/Contents/Resources
error: destination '/Users/admin/Documents/src/Soundflower/Build/InstallerRoot/Library/Extensions/Soundflower.kext/Contents/Resources/Soundflower.kext' is inside source '/Users/admin/Documents/src/Soundflower/Build/InstallerRoot/Library/Extensions/Soundflower.kext' (not copied) (in target 'Soundflower' from project 'Soundflower')

I noticed that the open source project comes with a build.rb file. So I tried to run that... and I'm getting the same results.
Any tips would be appreciated. In the meantime, I'm googling for these types of copy errors on a Mac.
Thanks.