message: doc: add c++17-enable to fuzzing instructions
diff: @@ -8,7 +8,7 @@ To quickly get started fuzzing Bitcoin Core using [libFuzzer](https://llvm.org/d
  $ git clone https://github.com/bitcoin/bitcoin
  $ cd bitcoin/
  $ ./autogen.sh
  -$ CC=clang CXX=clang++ ./configure --enable-fuzz --with-sanitizers=address,fuzzer,undefined
  +$ CC=clang CXX=clang++ ./configure --enable-fuzz --with-sanitizers=address,fuzzer,undefined --enable-c++17
  # macOS users: If you have problem with this step then make sure to read "macOS hints for
  # libFuzzer" on https://github.com/bitcoin/bitcoin/blob/master/doc/fuzzing.md#macos-hints-for-libfuzzer
  $ make
  @@ -103,7 +103,7 @@ You may also need to take care of giving the correct path for `clang` and
  Full configure that was tested on macOS Catalina with `brew` installed `llvm`:
  ```sh
  -./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined CC=/usr/local/opt/llvm/bin/clang CXX=/usr/local/opt/llvm/bin/clang++ --disable-asm
  +./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined CC=/usr/local/opt/llvm/bin/clang CXX=/usr/local/opt/llvm/bin/clang++ --disable-asm --enable-c++17
  ```
  Read the [libFuzzer documentation](https://llvm.org/docs/LibFuzzer.html) for more information. This [libFuzzer tutorial](https://github.com/google/fuzzing/blob/master/tutorial/libFuzzerTutorial.md) might also be of interest.
  @@ -121,7 +121,7 @@ $ git clone https://github.com/google/afl
  $ make -C afl/
  $ make -C afl/llvm_mode/
  $ ./autogen.sh
  -$ CC=$(pwd)/afl/afl-clang-fast CXX=$(pwd)/afl/afl-clang-fast++ ./configure --enable-fuzz
  +$ CC=$(pwd)/afl/afl-clang-fast CXX=$(pwd)/afl/afl-clang-fast++ ./configure --enable-fuzz --enable-c++17
  $ make
  # For macOS you may need to ignore x86 compilation checks when running "make". If so,
  # try compiling using: AFL_NO_X86=1 make
  @@ -148,7 +148,7 @@ $ git clone https://github.com/google/honggfuzz
  $ cd honggfuzz/
  $ make
  $ cd ..
  -$ CC=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang++ ./configure --enable-fuzz --with-sanitizers=address,undefined
  +$ CC=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang++ ./configure --enable-fuzz --with-sanitizers=address,undefined --enable-c++17
  $ make
  $ mkdir -p inputs/
  $ honggfuzz/honggfuzz -i inputs/ -- src/test/fuzz/process_message
  