This checks the `previous_work_products` data from the dep-graph and
tries to simply copy a `.o` file if possible. We also add new
work-products into the dep-graph, and create edges to/from the dep-node
for a work-product.
The data tracked here was meant to compare the output of the
translation item collector to the set of translation items found
by the on-demand translator.
Functions and method are declared ahead-of-time, including generic ones.
Closures are not considered trans items anymore, instead they are
translated on demands.
Casual grepping revealed some places in the codebase (some of which
antedated `if let`'s December 2014 stabilization in c200ae5a) where we
were using a match with a `None => ()` arm where (in the present
author's opinion) an `if let` conditional would be more readable. (Other
places where matching to the unit value did seem to better express the
intent were left alone.)
It's likely that we don't care about making such trivial,
non-functional, sheerly æsthetic changes.
But if we do, this is a patch.
When reuing a definition across codegen units, we obviously cannot use
internal linkage, but using external linkage means that we can end up
with multiple conflicting definitions of a single symbol across
multiple crates. Since the definitions should all be equal
semantically, we can use weak_odr linkage to resolve the situation.
Fixes#32518
