With no c++ code there is no point showing CXXFLAGS.

configure.ac

@@ -262,7 +262,6 @@ echo
 echo "Compilation............: make (or gmake)"
 echo "  CPPFLAGS.............: $CPPFLAGS"
 echo "  CFLAGS...............: $CFLAGS"
-echo "  CXXFLAGS.............: $CXXFLAGS"
 echo "  LDFLAGS..............: $LDFLAGS"
 echo
 echo "Installation...........: make install (as root if needed, with 'su' or 'sudo')"