compiler: Misc compiler improvements

[FabioLuporini]

Mostly to support new features in PRO

[codecov]

Codecov Report

Attention: Patch coverage is 78.83212% with 29 lines in your changes are missing coverage. Please review.

Project coverage is 86.83%. Comparing base (10963f3) to head (b6f1a08).

Files	Patch %	Lines
conftest.py	65.90%	14 Missing and 1 partial ⚠️
devito/arch/archinfo.py	53.33%	7 Missing ⚠️
devito/data/allocators.py	81.81%	4 Missing ⚠️
devito/mpi/distributed.py	88.23%	2 Missing ⚠️
devito/types/grid.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2380      +/-   ##
==========================================
- Coverage   86.87%   86.83%   -0.05%     
==========================================
  Files         234      234              
  Lines       43914    43982      +68     
  Branches     8109     8125      +16     
==========================================
+ Hits        38151    38191      +40     
- Misses       5058     5085      +27     
- Partials      705      706       +1     

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