Code:
all: $(TARGETS)
$(CC) -o $@ $^ $(LDLIBS) $(CFLAGS)
@echo Server && Client OK
$@ expands to the name of the target, so the second line causes gcc to make an executable called "all". I don't think you need this line at all.
&& is a shell operator, so the last line echo's "Server", then tries to execute a command called Client, you should write
Code:
@echo "Server && Client OK"
or
@echo Server and Client OK