fuzz: compile xdiff.cc with -std=c++17
Otherwise the build would fail as follows:
In file included from xdiff.cc:13:
./fuzzutil.h:23:10: fatal error: 'third_party/absl/types/optional.h' file not
found
#include "third_party/absl/types/optional.h"
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true