Cannot compile depends library- bitcoin v0.21.0

I'm trying to compile the depends library of bitcoin v0.21.0 on Ubuntu 20.04. When I'm running the make command, I'm receiving this error: funcs.mk:265: *** empty variable name. Stop.

What is the meaning of the error and how can I resolve it?

funcs.mk:265: *** empty variable name.  Stop.

What is the meaning of the error ...

It means that line 265 of funcs.mk contains an equals sign but the item to its left is not a valid variable name. Stop means make was unable to continue due to this error.

... and how can I resolve it?

By studying line 265.

Likely there is something earlier or externally that causes some construction here to not contain what it should.

You may need to ensure you have the latest versions of make and other resources using something like sudo apt-get update && sudo apt-get dist-upgrade