[OpenACC] Supporting Device Specific Clauses

[Sebastian Galindo]

Hi,

I'm a GSoC contributor this year and I'm implementing the device_type   
clause for some directives. For now I'm leaving the implementation      
working without the 'grouping' or device-specific clauses as the        
OpenACC spec recommend.                                                 

I saw a couple of comments regarding the integration of the clause, for 
example:                                                                

> /*TODO Things are conceptually wrong here: 'loop' clauses may be      
> hidden behind 'device_type', so we have to defer a lot of processing  
> until we're in the offloading compilation. "Fortunately", GCC doesn't 
> support the OpenACC 'device_type' clause yet, so we get away that. */ 

Or:

>  /* TODO: This will need amending when device_type is implemented. */

I would be interested in fully implementing the device_type as part     
of the last part in my GSoC project (as long as my mentors are ok       
with that) but I'm even more interested in getting some context         
regarding the challenges that device_type clause would imply and how to 
actually implement the device-specific clauses (maybe having multiple   
gfc_omp_clauses instances in the case of Fortran? I don't know).        

Let me know if there is any comment on this.

Thanks! Sebastian