lang/rust: Update to 1.34.1

• Add stdsimd patches from D19940 to attempt to unbreak powerpc64, armv{6,7} [1]

Changes: https://blog.rust-lang.org/2019/04/25/Rust-1.34.1.html
PR: 237507 [1]
Submitted by: mikael.urankar@gmail.com [1]
Reviewed by: jbeich [1]
Tested by: pkubaj (stdsimd patches with 1.34.0 on powerpc64) [1]
With hat: rust
Differential Revision: https://reviews.freebsd.org/D19940 [1]