Slightly modify the public domain license to keep it in the public domain, but make it clear that even when dedications might not be recognized that the code is still usable. Given that this isn't dual-licensing under a different license, I'm hoping this will be acceptable.

docs/stb_howto.txt

@@ -165,9 +165,9 @@ public domain declarations aren't necessary recognized
 in the USA and some other locations. For that reason,
 I recommend a declaration along these lines:
 
-// This software is in the public domain. Where that dedication is not
-// recognized, you are granted a perpetual, irrevocable license to copy
-// and modify this file as you see fit.
+// This software is dual-licensed to the public domain and under the following
+// license: you are granted a perpetual, irrevocable license to copy, modify,
+// publish, and distribute this file as you see fit.
 
 I typically place this declaration at the end of the initial
 comment block of the file and just say 'public domain'

docs/why_public_domain.md

@@ -95,9 +95,9 @@ public domain declarations aren't necessary recognized
 in the USA and some other locations. For that reason,
 I recommend a declaration along these lines:
 
-// This software is in the public domain. Where that dedication is not
-// recognized, you are granted a perpetual, irrevocable license to copy
-// and modify this file as you see fit.
+// This software is dual-licensed to the public domain and under the following
+// license: you are granted a perpetual, irrevocable license to copy, modify,
+// publish, and distribute this file as you see fit.
 
 I typically place this declaration at the end of the initial
 comment block of the file and just say 'public domain'