I've just pushed the following, so that gzip builds and passes "make distcheck" when using GCC 7:
maint: avoid unwarranted "make syntax-check" failure
gnulib: update to latest
http://git.savannah.gnu.org/cgit/gzip.git/commit/?id=684cc5eb56437028da0171b53053f60ccda85f9f
http://git.savannah.gnu.org/cgit/gzip.git/commit/?id=56eb6940aff95bbe5105e8e8c7eff20d176c7dd0
