I am packaging optipng (http://optipng.sourceforge.net/) with the
gnu-build-system, and its configure script does not like being passed
CONFIG_SHELL. It fails with the following error:

./configure: error: unknown option: CONFIG_SHELL=/gnu/store/ykzwykkvr2c80rw4l1qh3mvfdkl7jibi-bash-4.3.42/bin/bash

Can we allow disabling of CONFIG_SHELL by passing some keyword argument
to the configure phase? Right now, the CONFIG_SHELL argument is always
passed to ./configure, and the only way to get around this is to replace
the configure phase for the optipng package with a specialized function
that does not pass CONFIG_SHELL. That seems like too much work, and it
will be nice if we can just disable CONFIG_SHELL with a keyword argument.

Regards,
Arun Isaac.