Add fuzz stuff ("backend/tests/fuzz"), including OSS-Fuzz

"Dockerfile" etc
PDF417: lessen some debug verbosity
gif: use "gif_" prefix; some code fiddling

backend/tests/fuzz/build.sh

@@ -0,0 +1,42 @@
+#!/bin/bash -eu
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+################################################################################
+
+# build project
+mkdir build
+cd build
+cmake -DZINT_STATIC=ON -DZINT_SHARED=OFF \
+    -DZINT_USE_PNG=OFF -DZINT_USE_QT=OFF -DZINT_FRONTEND=OFF \
+    -DCMAKE_BUILD_TYPE=Debug \
+    ..
+make -j$(nproc)
+
+# build fuzzers
+bd=$SRC/zint/backend
+
+fd=$bd/tests/fuzz
+fn=fuzz_data
+$CC $CFLAGS -fsanitize=fuzzer-no-link -I${bd} $fd/${fn}.c -c -o $WORK/${fn}.o
+$CXX $CXXFLAGS $WORK/${fn}.o -o $OUT/${fn} \
+    $LIB_FUZZING_ENGINE -lm -lzint -Lbackend
+cp $fd/${fn}_seed_corpus.zip $OUT
+
+fn=fuzz_gs1
+$CC $CFLAGS -fsanitize=fuzzer-no-link -I${bd} $fd/${fn}.c -c -o $WORK/${fn}.o
+$CXX $CXXFLAGS $WORK/${fn}.o -o $OUT/${fn} \
+    $LIB_FUZZING_ENGINE -lm -lzint -Lbackend
+cp $fd/${fn}_seed_corpus.zip $OUT
+cp $fd/${fn}.dict $OUT