Filed under reasons the #Solaris Bourne shell (/bin/sh on Solaris 10 & older, /usr/sunos/bin/sh on Solaris 11) drove people mad:
https://cgit.git.savannah.gnu.org/cgit/autoconf.git/commit/?id=b1eb59a78a0d5f1bdb10bc8869d5e48f73dcbc7a
https://lists.gnu.org/archive/html/autoconf/2025-07/msg00004.html