at some point after commit 61c843815e7d23110e089b45ab4be270bc2a415d (tag: v9_12_0rc1)
and before commit4c8cd59241040e161e6db3e58216e66e1f69c874 (HEAD -> v9_12, origin/v9_12, gitlab/v9_12)

When you run ./configure --without-openssl && make, the make fails:
In file included from hmac_link.c:44:
./dst_openssl.h:18:10: fatal error: 'openssl/err.h' file not found
#include <openssl/err.h>

(This was tested on OSX, but I see no evidence that it wouldnt happen with all platforms)