[DRE-maint] Bug#1031307: ruby-oj: buf.h #includes mem.h that is not shipped

[Adrian Bunk]

Package: ruby-oj
Version: 3.14.1-3
Severity: serious
Tags: ftbfs
Control: affects -1 src:ruby-oj-introspect

https://buildd.debian.org/status/fetch.php?pkg=ruby-oj-introspect&arch=armhf&ver=0.7.1-3&stamp=1676220273&raw=0

...
In file included from /usr/include/ruby-3.1.0/vendor_ruby/oj/parser.h:10,
                 from introspect.c:3:
/usr/include/ruby-3.1.0/vendor_ruby/oj/buf.h:8:10: fatal error: mem.h: No such file or directory
    8 | #include "mem.h"
      |          ^~~~~~~
...