Followup to PR #16477: a run-pass regression test for Issue #15750.
librustc: Implement simple `where` clauses.

These `where` clauses are accepted everywhere generics are currently
accepted and desugar during type collection to the type parameter bounds
we have today.

A new keyword, `where`, has been added. Therefore, this is a breaking
change. Change uses of `where` to other identifiers.

[breaking-change]
auto merge of #16424 : pcwalton/rust/where-clauses, r=nikomatsakis

These `where` clauses are accepted everywhere generics are currently
accepted and desugar during type collection to the type parameter bounds
we have today.

A new keyword, `where`, has been added. Therefore, this is a breaking
change. Change uses of `where` to other identifiers.

[breaking-change]

r? @nikomatsakis (or whoever)
auto merge of #16494 : pnkfelix/rust/fsk-quotstx-followup, r=alexcrichton

Followup to PR #16477: a run-pass regression test for Issue #15750.
Change how libgetopts handles options grouped together

As soon as an option is found that takes an argument, consume the rest
of the string and store it into i_arg. Previously this would only happen
if the character after the option was not a recognized option.

Addresses issue #16348