Accept old mixed-case toolchain_env_var variable names

[adamgreig]

See #728 and #687.

Having done this, though, I wonder if having the toolchain env vars be uppercase would be better in general, even if we maintain an old/deprecated mixed-case name? All the tool overrides are already in uppercase, and using all-uppercase environment variables is a widely used convention. We could extend deprecated_toolchain_env_var to cover both NMIGEN_ENV_Diamond and AMARANTH_ENV_Diamond, with AMARANTH_ENV_DIAMOND being the nominal name, used first if multiple are set.

I don't especially mind, happy to just take this as-is (or with whatever changes you want), but maybe it would be more consistent to deliberately change to all-uppercase for 0.4.

[whitequark]

We could extend deprecated_toolchain_env_var to cover both NMIGEN_ENV_Diamond and AMARANTH_ENV_Diamond, with AMARANTH_ENV_DIAMOND being the nominal name, used first if multiple are set.

LGTM

[codecov-commenter]

Codecov Report

Merging #729 (a7dfa3e) into main (db24a14) will decrease coverage by 0.01%.
The diff coverage is 37.50%.

@@            Coverage Diff             @@
##             main     #729      +/-   ##
==========================================
- Coverage   81.17%   81.15%   -0.02%     
==========================================
  Files          49       49              
  Lines        6535     6539       +4     
  Branches     1567     1569       +2     
==========================================
+ Hits         5305     5307       +2     
- Misses       1037     1038       +1     
- Partials      193      194       +1     

Impacted Files	Coverage Δ
amaranth/build/plat.py	26.31% <37.50%> (+0.33%)	⬆️
amaranth/build/run.py	21.73% <0.00%> (ø)

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[adamgreig]

I've updated to accept the old case for the name alongside the NMIGEN version and the new uppercase version. If multiple variables are specified then the deprecated versions are executed first, followed by the new uppercase version, which means it should be the one to actually take effect - which is the same behaviour as before when both NMIGEN and AMARANTH versions were specified.

I've only tested the ECP5 toolchain as I don't have tools installed for the others.

[whitequark]

Thank you very much!