GitLab

Fixes #106.

* m4/gccwarn.m4: Use -Wzero-as-null-pointer-constant if supported.
* src/bin/autfilt.cc, src/bin/common_aoutput.cc,
src/bin/common_finput.cc, src/bin/common_finput.hh,
src/bin/common_output.cc, src/bin/common_output.hh,
src/bin/common_post.cc, src/bin/common_r.hh, src/bin/common_range.hh,
src/bin/common_setup.cc, src/bin/common_trans.cc, src/bin/dstar2tgba.cc,
src/bin/genltl.cc, src/bin/ltl2tgba.cc, src/bin/ltl2tgta.cc,
src/bin/ltlcross.cc, src/bin/ltldo.cc, src/bin/ltlfilt.cc,
src/bin/ltlgrind.cc, src/bin/randaut.cc, src/bin/randltl.cc,
src/bin/spot-x.cc, src/kripke/kripkeexplicit.cc, src/ltlast/formula.cc,
src/ltlvisit/randomltl.cc, src/ltlvisit/randomltl.hh,
src/ltlvisit/relabel.cc, src/ltlvisit/relabel.hh,
src/ltlvisit/simplify.cc, src/ltlvisit/snf.hh, src/misc/fixpool.hh,
src/misc/mspool.hh, src/misc/hash.hh, src/misc/optionmap.cc,
src/misc/satsolver.cc, src/misc/tmpfile.cc, src/misc/tmpfile.hh,
src/priv/bddalloc.cc, src/ta/ta.hh, src/t...