Need help with strange rubygem: oj-introspect

Dear all,

I currently try to prepare an upgrade to gitlab-ce 15.6 but one port 
currently blocks me and maybe someone can help my, as I'm currently out 
of ideas.

The problem is with oj-introspect:
https://rubygems.org/gems/oj-introspect

It expects header files the port rubygem-oj does not install.
Not sure if is this a problem that should be fixed upstream, but before 
I report there anything, I would like to get the port running.
What I did now is adding a postinstall target that includes the headers 
files and I can continue with the process:
https://gitlab.fechner.net/mfechner/Gitlab/-/commit/15bc6ed3226ab4ee4cc55a6553c0238160e7f6a4#ac2c957b19f5793163b5c34e6ccc9891c2f8c475_16_16

But if I try to compile the gem oj-introspect:
https://gitlab.fechner.net/mfechner/Gitlab/-/tree/42c09fd7c25d1375c3c3e4513b8cba9cb16f3987/devel/rubygem-oj-introspect

I get a linker error:

current directory: /wrkdirs/usr/ports/devel/rubygem-oj-introspect/work/stage/usr/local/lib/ruby/gems/3.0/gems/oj-introspect-0.7.1/ext/oj-introspect
make DESTDIR\= sitearchdir\=./.gem.20221220-79616-gouqlr sitelibdir\=./.gem.20221220-79616-gouqlr
compiling introspect.c
linking shared-object oj/introspect/introspect_ext.so
ld: error: unknown argument '-U'
ld: error: unknown argument '-U'
ld: error: unknown argument '-U'
ld: error: cannot open _oj_init_usual: No such file or directory
ld: error: cannot open _oj_parser_new: No such file or directory
ld: error: cannot open _oj_parser_set_option: No such file or directory
cc: error: linker command failed with exit code 1 (use -v to see invocation)
*** Error code 1

The full buildlog is here:
https://pkg.fechner.net/data/131amd64-gitlab/2022-12-20_10h29m08s/logs/errors/rubygem-oj-introspect-0.7.1.log

Does anyone have an idea how to fix this?

Thanks a lot for any tips!

Gruß
Matthias

-- 

"Programming today is a race between software engineers striving to
build bigger and better idiot-proof programs, and the universe trying to
produce bigger and better idiots. So far, the universe is winning." --
Rich Cook