Provide scripts to run fuzzers on oss-fuzz

This allows us to reuse the toolchains and fuzzers with oss-fuzz or
clusterfuzzlite.

.clusterfuzzlite/Dockerfile

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+# c-toxcore Clusterfuzzlite build environment
+
+FROM gcr.io/oss-fuzz-base/base-builder
+
+RUN apt-get update && \
+    apt-get -y install --no-install-suggests --no-install-recommends \
+    cmake libtool autoconf automake pkg-config
+
+RUN git clone --depth 1 --branch 1.0.18 https://github.com/jedisct1/libsodium libsodium
+RUN cd libsodium && ./autogen.sh && ./configure --enable-shared=no && make && make install
+
+# Copy your project's source code.
+COPY . $SRC/c-toxcore
+# Working directory for build.sh.
+WORKDIR $SRC/c-toxcore
+# Copy build.sh into $SRC dir.
+COPY ./.clusterfuzzlite/build.sh $SRC/

.clusterfuzzlite/build.sh

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+#!/bin/bash -eu
+
+# out of tree build
+cd $WORK
+
+ls /usr/local/lib/
+
+# Debug build for asserts
+cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER="$CC" \
+  -DCMAKE_CXX_COMPILER="$CXX" \
+  -DCMAKE_C_FLAGS="$CFLAGS" \
+  -DCMAKE_CXX_FLAGS="$CXXFLAGS" \
+  -DCMAKE_EXE_LINKER_FLAGS="$LIB_FUZZING_ENGINE" \
+  -DBUILD_TOXAV=OFF -DENABLE_SHARED=NO -DBUILD_FUZZ_TESTS=ON \
+  -DDHT_BOOTSTRAP=OFF -DBOOTSTRAP_DAEMON=OFF $SRC/c-toxcore
+
+# build fuzzer target
+cmake --build ./ --target bootstrap_fuzzer
+
+# copy to output files
+cp $WORK/bootstrap_fuzzer $OUT/