83eb264273
CFG construction takes a large amount of time and memory, especially for large constants. If such a constant contains no actions on lvalues, it can't have borrowck problems and can be ignored by it. This removes the 4.9GB borrowck peak from #36799. It seems that HIR had grown by 300MB and MIR had grown by 500MB from the last massif collection and that remains to be investigated, but this at least shaves the borrowck peak.