This has less to do with natural opinions regarding code organization and more to do with the fact that including, modularizing, and distributing C code has historically been a pain in the ass which is ameliorated by shoving everything into a single file.

/? single header https://hn.algolia.com/?q=single%20header

/? header-only https://hn.algolia.com/?q=header-only

/? c header https://hn.algolia.com/?q=c+header

EDIT: Sorry, I missed the "header" part (and the irony).

At least once, here you go:

https://news.ycombinator.com/item?id=48053570

Ok, I just submitted it myself but I could not believe it never had been submitted before. It is from 1997 and was pretty popular for some time. I think it even was built into Google Picasa for sime time.