[Bug #19831] Remove duplicate library options

`$(MAINLIBS)` should be included in `$(LIBRUBYARG)` in cases it is
needed.

template/Makefile.in

@@ -292,7 +292,7 @@ miniruby$(EXEEXT):
 $(PROGRAM):
 		@$(RM) $@
 		$(ECHO) linking $@
-		$(Q) $(PURIFY) $(CC) $(EXE_LDFLAGS) $(XLDFLAGS) $(MAINOBJ) $(EXTOBJS) $(LIBRUBYARG) $(MAINLIBS) $(EXTLIBS) $(OUTFLAG)$@
+		$(Q) $(PURIFY) $(CC) $(EXE_LDFLAGS) $(XLDFLAGS) $(MAINOBJ) $(EXTOBJS) $(LIBRUBYARG) $(EXTLIBS) $(OUTFLAG)$@
 		$(Q) $(POSTLINK)
 
 $(PROGRAM): @XRUBY_LIBPATHENV_WRAPPER@