Some notes on GNU Make. I always have to look-up these in the manual. Here now for my own convenience.
GNU Make automatic variables:
The file name of the target of the rule.
The target member name
The name of the first prerequisite.
The names of all the prerequisites that are newer.
The names of all the prerequisites.
To include files in Makefile only if they exist:
ifneq ($(wildcard _incfile_),) include _incfile_ endif