Conflict between make --touch and multi-architecture build strategy

[Deshaies-Jacques, Martin (EC)]

Hi,

I have implemented the method described on [Paul D. Smith's 
blog](http://make.mad-scientist.net/papers/multi-architecture-builds/) for 
multi-architecture builds.
This was done for a fortran data assimilation library used at the Canadian 
Meteorological Center.
The project being in fortran 90, there is no clear separation between 
declaration of interfaces and implementation, such that if only implementation 
of a function is modified there is no simple way to tell `make` not to 
recompile every dependent objects but simply the one modified and proceed with 
relinking.

We tried to use `make --touch` to indicate not to recompile certain objects for 
these case, but through the [`target.mk`  out-of-tree 
strategy](http://make.mad-scientist.net/papers/multi-architecture-builds/#target.mk)
 it also touches empty files (named after the targets of the `make --touch` in 
the `Makefile` directory, cluttering it with a lot of useless files...

I created a simplified `Makefile` that reproduce that issue, which could be 
accessed at

https://gitlab.com/martn/makeTouchIssue

Would you be aware of a way to resolve that and keep the out-of-tree 
compilation working?

For sake of completeness, I include here the description of the simplified 
reproduction of the potential issue that one would find in the gitlab project 
`README.md`
The gitlab project itself can be cloned to reproduce the simplified usecase 
issue.


Regards,

--
Martin Deshaies-Jacques

Spécialiste en sciences physiques | Physical sciences specialist
Environnement et Changement Climatique Canada | Environment and Climate Change 
Canada
Recherche en qualité de l'air | Air Quality Research Division
2121, Autoroute transcanadienne, Dorval (Québec) H9P 1J3
514.421.5304

README.md
Description: README.md