Commit 0a96acf251baa5c9dd042d093ab2bf8fcee10502 broke compatibility with
hunspell versions earlier than v1.5.1. v1.5.1 is was released Nov 2016,
thus only two years old.
This patch restores the build with hunspell versions provided on more
conservative platforms (e.g. CentOS 6.8, which provides hunspell v1.2.x)