Unable to build S3 example using provided instructions

The instructions say to use the provided Dockerfile to build the S3 example. However, it looks like something has changed as the build now fails:

```
# make
Scanning dependencies of target encoder
[ 50%] Building CXX object CMakeFiles/encoder.dir/main.cpp.o
[100%] Linking CXX executable encoder
/usr/include/c++/9.3.0/ext/string_conversions.h: In function '__to_xstring.constprop':
/usr/include/fortify/stdio.h:70:28: error: inlining failed in call to always_inline 'vsnprintf': function body can be overwritten at link time
70 | _FORTIFY_FN(vsnprintf) int vsnprintf(char *__s, size_t __n, const char *__f,
| ^
/usr/include/c++/9.3.0/ext/string_conversions.h:111:32: note: called from here
111 | const int __len = __convf(__s, __n, __fmt, __args);
| ^
lto-wrapper: fatal error: /usr/bin/c++ returned 1 exit status
compilation terminated.
/usr/lib/gcc/x86_64-alpine-linux-musl/9.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/encoder.dir/build.make:116: encoder] Error 1
make[1]: *** [CMakeFiles/Makefile2:97: CMakeFiles/encoder.dir/all] Error 2
make: *** [Makefile:104: all] Error 2
```

Please provide updated instructions for building the S3 example.