#374 support passing MODINFO to configure

[Micha Lenk]

Dear maintainer of lirc,

right now the lirc build system doesn't honor the MODINFO variable for overriding which modinfo binary to use during build. This is an issue in terms of support for reproducible builds (see more on https://reproducible-builds.org/), so it was reported to the maintainers of the lirc package in Debian:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=979021

The attached patch contributed by Vagrant Cascadian fixes that by changing configure to accept the
MODINFO variable. In Debian builds this would be used to pass hard-coded SH_PATH and MODINFO variables to configure.

Please merge the patch so that more users could benefit from these changes and so that it is part of future lirc releases.

Thanks a lot for considering.

Regards,
Micha