Since 'mkmf' is already in the fstring table as that exists in
the source; so I'll at least have to squash this on top for
Ruby <=2.5:
diff --git a/ext/unicorn_http/extconf.rb b/ext/unicorn_http/extconf.rb
index 5b7a8ca..d5f81fb 100644
--- a/ext/unicorn_http/extconf.rb
+++
String#-@ deduplicates strings starting with Ruby 2.5.0
Hash#[]= deduplicates strings starting in Ruby 2.6.0-rc1
This allows us to save a small amount of memory by sharing
objects with other parts of the stack (e.g. Rack).
---
RFC because I've only lightly-tested this and only with Ruby