* configure.ac: Add -Wabi to the list of disabled warning
options. For the details, see
http://lists.gnu.org/archive/html/emacs-devel/2018-08/msg00123.html.
nw="$nw -Wsync-nand" # irrelevant here, and provokes ObjC warning
nw="$nw -Wunsafe-loop-optimizations" # OK to suppress unsafe optimizations
nw="$nw -Wbad-function-cast" # These casts are no worse than others.
+ nw="$nw -Wabi" # Not useful, perceived as noise
# Emacs doesn't care about shadowing; see
# <https://lists.gnu.org/r/emacs-diffs/2011-11/msg00265.html>.