This is an easy place to start, and these functions are probably safe.
Please review with it in mind that I want to add more fuzz tests later.

While the fuzz tests are included in CPython and compiled / tested on a
very basic level inside CPython itself, the actual fuzzing happens as
part of oss-fuzz (https://github.com/google/oss-fuzz). The reason to
include the tests in CPython is to make sure that they're maintained
as part of the CPython project, especially when (as some will) they
use internal implementation details in the test.

(This will be necessary sometimes because e.g. the fuzz test should
never enter Python's interpreter loop, whereas some APIs only expose
themselves publicly as Python functions.)

This particular set of changes is part of testing Python's builtins,
tracked internally at Google by b/37562550.

… occurs.

I'm still not happy with how many times I need to repeat the fuzz test name.
This can go wrong way too easily. :/

It's possible there's a way to compile this with clang and then link it with
clang++, but I don't know how to do that.

Specifically, compilation fails with this:

    $CC $CFLAGS \
        -D _Py_FUZZ_ONE -D _Py_FUZZ_$fuzz_test \
        -Wno-unused-function \
        $($OUT/bin/python3-config --cflags) -g -O1 \
        $FUZZ_DIR/fuzzer.c -o $OUT/$fuzz_test -lFuzzingEngine \
        $($OUT/bin/python3-config --ldflags)

With errors like:

    /usr/local/bin/../include/c++/v1/new:234: undefined reference to `operator delete(void*)'

But it works just fine with this:

    $CXX $CXXFLAGS \
        -D _Py_FUZZ_ONE -D _Py_FUZZ_$fuzz_test \
        -Wno-unused-function \
        $($OUT/bin/python3-config --cflags) -g -O1 \
        $FUZZ_DIR/fuzzer.c -o $OUT/$fuzz_test -lFuzzingEngine \
        $($OUT/bin/python3-config --ldflags)

Presumably there are ways to do this in C, so for expediency I'm doing it in C++
right now, with the minimal possible C++ changes (extern "C"), so that if I need
to change it back to C in code review, it won't be too hard.

(i.e. just to get increased confidence we won't immediately crash on fuzzing.)

I'm using s# because I'd like to minimize the diff between Python 2 and 3.