From SO.

Basic

current_dir = $(shell pwd)

Absolute path

current_dir = $(notdir $(shell pwd))

Flexible

Or if invoking Makefile from any directory, such as using includes to load a Makefile in another directory.

mkfile_path := $(abspath $(lastword $(MAKEFILE_LIST)))
current_dir := $(notdir $(patsubst %/,%,$(dir $(mkfile_path))))