Log Message:
Update rust to version 1.34.1.

Pkgsrc changes: basically none.  Build verified on NetBSD 8.0/i386.

Upstream changes:

Version 1.34.1 (2019-04-25)
===========================

* [Fix false positives for the `redundant_closure` Clippy lint][clippy/3821]
* [Fix false positives for the `missing_const_for_fn` Clippy lint][clippy/3844]
* [Fix Clippy panic when checking some macros][clippy/3805]

[clippy/3821]: https://github.com/rust-lang/rust-clippy/pull/3821
[clippy/3844]: https://github.com/rust-lang/rust-clippy/pull/3844
[clippy/3805]: https://github.com/rust-lang/rust-clippy/pull/3805