Understood, but no solution is in sight unfortunately.
It turns out that configure doesn’t play nicely with -Werror and whilst my code still compiles and works on Linux when compiled that way it’s mostly luck. OSX does not (in my house at least) come with such a large dollop of good fortune.
Were it not for the fact that I have code for other projects that will fail to build with -Werror embedded in my code tree there was a possibility that adding the following to the top level Makefile.am would have helped:
WARNINGS = -Werror -O2 -g warnings: $(MAKE) V=0 CFLAGS='$(WARNINGS)' CXXFLAGS='$(WARNINGS)' $(MAKE) V=0 CFLAGS='$(WARNINGS)' CXXFLAGS='$(WARNINGS)' $(check_PROGRAMS)
allowing me to run
$ make warnings
to build the system where warnings cause a compile error. In my case I don’t unfortunately see such a handy workaround.
On the positive side, I did at the same time discover that the option
AM_SILENT_RULES([yes])
in configure.ac significantly decreases the verbosity of the compilation process, so I shall tuck that one behind my ear for later.