devel/gn: update to version 1714.

Full changelog: https://github.com/cglogic/gn/compare/v1600...v1714

Changelog highlights:

• Rust compilation tool and toolchain support
• Teach gn to handle systems with > 64 processors
• Switch to C++17
• Support for RISC-V
• Improve support for frameworks in gn
• Speed up source file set operations

PR: 244307
Submitted by: o.hushchenkov@gmail.com (maintainer)