bug#19111: 25.0.50; 32 bits temacs.exe is linked with wrong image-base when built on 64 bit Windows host

[Glenn Morris]

https://www.gnu.org/software/autoconf/manual/autoconf-2.64/html_node/Shell-Substitutions.html
     
     ${#var}
     ${var%word}
     ${var%%word}
     ${var#word}
     ${var##word}
         Posix requires support for these usages, but they do not work with
         many traditional shells, e.g., Solaris 10 /bin/sh.
     
It's easy to replace this with something that we know is fine, using sed
or eval. So I'd do that. Cygwin is not a representative sample.