Enhancements:
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* allow env check to be bypassed when rendering (for c3i)  #2353
* provide mechanism for compiler version to be passed to compiler jinja2 function (match name with _version)  #2356

Bug fixes:
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* use host_subdir instead of build_subdir when setting selectors  #2345
* remove downloaded files from source cache if they failed at any download step  #2349
* fix variants being merged across multiple builds due to modification of global  #2350
* disable pyldd disagrees warning output for now  #2352