gnucash master: Fix build on Ubuntu-18.04.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/650f7901 (commit)
	from  https://github.com/Gnucash/gnucash/commit/7461cc2a (commit)



commit 650f7901cd406a70550769aa4e22fbc161b24aeb
Author: John Ralls <jralls at ceridwen.us>
Date:   Mon May 4 19:47:34 2020 -0700

    Fix build  on Ubuntu-18.04.



Summary of changes:
 CMakeLists.txt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)