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)