Feature request: require that .SUFFIXES is explicitly declared

[PhilipRoman]

There is an old way of declaring implicit rules for make, called "suffix rules". See https://www.gnu.org/software/make/manual/html_node/Suffix-Rules.html for documentation. Most of the time the default rules are unnecessary and can cause unexpected results when accidentally invoked.

Checkmake should have a rule that ensures that a target .SUFFIXES is explicitly declared.