Check for a case sensitive file system

This code from Android project:

# check for a case sensitive file system

ifneq (a,$(shell mkdir -p $(OUT_DIR) ; \
                echo a > $(OUT_DIR)/casecheck.txt; \
                    echo B > $(OUT_DIR)/CaseCheck.txt; \
                cat $(OUT_DIR)/casecheck.txt))
$(warning ************************************************************)
$(warning You are building on a case-insensitive filesystem.)
$(warning Please move your source tree to a case-sensitive filesystem.)
$(warning ************************************************************)
$(error Case-insensitive filesystems not supported)
endif