build: correct some targets and their rules to prevent unneeded rebuilds

Without this patch the binaries are linked anew and the manpage gets
recreated with every 'make' and 'make install' call, even if no changes
to the sources have happened.

Makefile

@@ -90,22 +90,22 @@ ifneq (,$(findstring Apple,$(shell $(CC) --version)))
 CFLAGS += -fstrict-aliasing -freorder-blocks -fsched-interblock
 endif
 
-all: $(BUILDDIR) $(BINS) vpnc.8
+all: $(BUILDDIR) $(addprefix $(BUILDDIR)/,$(BINS)) src/vpnc.8
 
 $(BUILDDIR):
 	@mkdir $@
 
-vpnc: $(OBJS) src/vpnc.o
-	$(CC) $(LDFLAGS) -o $(BUILDDIR)/$@ $^ $(LIBS)
+$(BUILDDIR)/vpnc: $(OBJS) src/vpnc.o
+	$(CC) $(LDFLAGS) -o $@ $^ $(LIBS)
 
-vpnc.8: src/vpnc.8.template src/makeman.pl vpnc
+src/vpnc.8: src/vpnc.8.template src/makeman.pl $(VPNC)
 	./src/makeman.pl $(VPNC)
 
-cisco-decrypt: src/cisco-decrypt.o src/decrypt-utils.o
-	$(CC) $(LDFLAGS) -o $(BUILDDIR)/$@ $^ $(LIBS)
+$(BUILDDIR)/cisco-decrypt: src/cisco-decrypt.o src/decrypt-utils.o
+	$(CC) $(LDFLAGS) -o $@ $^ $(LIBS)
 
-test-crypto: src/sysdep.o src/test-crypto.o src/crypto.o $(CRYPTO_OBJS)
-	$(CC) $(LDFLAGS) -o $(BUILDDIR)/$@ $^ $(LIBS)
+$(BUILDDIR)/test-crypto: src/sysdep.o src/test-crypto.o src/crypto.o $(CRYPTO_OBJS)
+	$(CC) $(LDFLAGS) -o $@ $^ $(LIBS)
 
 .depend: $(SRCS) $(BINSRCS)
 	$(CC) -MM $(SRCS) $(BINSRCS) $(CFLAGS) $(CPPFLAGS) > $@