devel/libcjson: Improve port
- Rework Makefile to follow Porters Handbook more closely
- Fix issues reported by DEVELOPER=yes
- Adjust CMAKE args to be readable and there's no need to list every possible option
- Compile to c89 standard as other distros and upstream [1]
- Drop static libs, nothing in tree uses them
1: https://github.com/DaveGamble/cJSON/blob/v1.7.18/CMakeLists.txt#L22
https://github.com/DaveGamble/cJSON/pull/836
PR: 279133
Approved by: portmgr (maintainer timeout, 2+ weeks)