Test eval and exec timing of Makefile.

T1=$(shell date)
D1=$(shell sleep 1)
T2=$(shell date)
D2=$(shell sleep 1)
T3:=$(shell date)
D3=$(shell sleep 1)
all:
        @date
        @sleep 1
        @date
        @sleep 1
        @echo $(shell date)
        $(shell sleep 1)
        @echo $(shell date)
        @sleep 1
        @echo "T1: $(T1)"
        @sleep 1
        @echo "T2: $(T2)"
        @sleep 1
        @echo "T3: $(T3)"