[autobuild] adjust Makefile.am for FreeBSD

the cross-compile build rule does not seem to like $^ for lemon,
so specify lemon.c explicitly in the build command

(thx stbuehler for suggested workaround)

src/Makefile.am

@@ -10,7 +10,7 @@ TESTS=\
 	test_configfile$(EXEEXT)
 
 lemon$(BUILD_EXEEXT): lemon.c
-	$(AM_V_CC)$(CC_FOR_BUILD) $(CPPFLAGS_FOR_BUILD) $(CFLAGS_FOR_BUILD) $(LDFLAGS_FOR_BUILD) -o $@ $^
+	$(AM_V_CC)$(CC_FOR_BUILD) $(CPPFLAGS_FOR_BUILD) $(CFLAGS_FOR_BUILD) $(LDFLAGS_FOR_BUILD) -o $@ lemon.c
 
 lighttpd_angel_SOURCES=lighttpd-angel.c