When building the test part of FLTK with configure+make this warning now appears :

Makefile:318: warning: ignoring prerequisites on suffix rule definition

It's caused by line #317 of test/Makefile

.fl.cxx .fl.h:    ../fluid/fluid$(EXEEXT)
which is a suffix rule containing a prerequisite. That seems to not make sense

for make, as explained in

   https://www.gnu.org/software/make/manual/html_node/Error-Messages.html

"According to POSIX, a suffix rule cannot contain prerequisites. If a rule that could be a suffix rule has prerequisites it is interpreted as a simple explicit rule, with an odd target name. This requirement is obeyed when POSIX-conforming mode is enabled (the .POSIX target is defined). In versions of GNU make prior to 4.3, no warning was emitted and a suffix rule was created, however all prerequisites were ignored and were not part of the suffix rule. Starting with GNU make 4.3 the behavior is the same, and in addition this warning is generated. In a future version the POSIX-conforming behavior will be the only behavior: no rule with a prerequisite can be suffix rule and this warning will be removed."

My suggestion to remove this warning is that the prerequisite must just be removed,

to obtain

.fl.cxx .fl.h: 

At any rate, the prerequisite is not operational, because the make command

fails if fluid is not present in ../fluid/. So, we loose nothing by removing it.

Am I overlooking something?