For some strange reason, there are five hex 09 bytes in stunnel-4.26/src/Makefile.am. This broke my Cygwin build: I remove the Windows-only stuff from this file for Cygwin, and diff captured the 0x09 characters that got removed, but then when I later tried to apply the patch, patch choked on them.
It seems that each of these bytes should really be 0x0A. Strange.
Andrew.