www/libnghttp2: Update to 1.51.0
- Switch to CMake
- Modernize Makefile to follow Porters Handbook more closely
Poudriere test run by bofh (thanks!)
Changelog: https://github.com/nghttp2/nghttp2/releases/tag/v1.51.0
PR: 268536
Approved by: portmgr (maintainer timeout, 2+ weeks)