Properly static lib packaging

Fixes #18574
Rename deprecated EnumSet methods in unit tests.
Add BitXor to EnumSet.
Add tests for BitAnd and BitXor.
Reword &str coercion into viewing
Fix handling of for loop patterns in regionck

When establishing region links within a pattern, use the mem-cat
of the type the pattern matches against (that is, the result
of `iter.next()`) rather than that of the iterator type.

Closes #17068
Closes #18767
Add regression for #17068
Add regression for #18767
mk: Fix Windows cross-build prefix
As of 4.9.2, gcc started passing -fno-lto to collect2, or to ld if collect2 cannot be found.  The latter is the case for our bundles, because we don't include collect2.  Unfortunately, ld does not understand this option and errors out.
On the bright side, -fno-use-linker-plugin still works to suppress gcc's LTO, so we can drop -fno-lto.
Move gcc back to rustlib\<triple>\bin
Prefer bundled linker.
Make Int inherit from Ord.

Previously Int inherited from PartialOrd (via Primitive)
but not Ord.  But integers have a total order, so
inheriting from Ord is appropriate. Fixes #18776.
Include some of the more popular Windows import libs into the bundle.
Fix upvars sometimes not being marked as used mutably

Drill down the loan path for McDeclared references as well since
it might lead to an upvar.  Closes #18769
Update test to cover #18769
First stage of struct variant field visibility changes

We need a snapshot before the parser can be adjusted.
auto merge of #18756 : jbcrail/rust/add-enum-set-bitxor, r=alexcrichton

I implemented BitXor, and also added tests for BitAnd and BitXor.

cc #18424
Add Encodable and Decodable for VecMap
auto merge of #18762 : mdinger/rust/str_coerce, r=steveklbanik

I had slight confusion when using this as a reference and was told it was imprecise. Most of the rewording was suggested by @huonw.

cc @steveklabnik