add ossfuzz build script

tests/ossfuzz.sh

@@ -0,0 +1,25 @@
+#!/bin/bash -eu
+# This script is meant to be run by
+# https://github.com/google/oss-fuzz/blob/master/projects/stb/Dockerfile
+
+$CXX $CXXFLAGS -std=c++11 -I. -DSTBI_ONLY_PNG  \
+    $SRC/stb/tests/stbi_read_fuzzer.c \
+    -o $OUT/stb_png_read_fuzzer $LIB_FUZZING_ENGINE
+
+$CXX $CXXFLAGS -std=c++11 -I. \
+    $SRC/stb/tests/stbi_read_fuzzer.c \
+    -o $OUT/stbi_read_fuzzer $LIB_FUZZING_ENGINE
+
+find $SRC/stb/tests/pngsuite -name "*.png" | \
+     xargs zip $OUT/stb_png_read_fuzzer_seed_corpus.zip
+
+cp $SRC/stb/tests/stb_png.dict $OUT/stb_png_read_fuzzer.dict
+
+tar xvzf $SRC/stb/jpg.tar.gz --directory $SRC/stb/tests
+tar xvzf $SRC/stb/gif.tar.gz --directory $SRC/stb/tests
+
+find $SRC/stb/tests -name "*.png" -o -name "*.jpg" -o -name ".gif" | \
+     xargs zip $OUT/stbi_read_fuzzer_seed_corpus.zip
+
+echo "" >> $SRC/stb/tests/gif.dict
+cat $SRC/stb/tests/gif.dict $SRC/stb/tests/stb_png.dict > $OUT/stbi_read_fuzzer.dict