This makes Makefile POSIX-compliant by getting rid of non-standard
operators. When there's a need for an user to build project with
values from environment variables, they can pass -e flag to make.
I am in fact not entirely sure that this is desirable. I'd be curious:
what make are you using that you'd need this? I am pretty sure there is
very little software out there that you could actually build with pure
POSIX make?
Conrad