Can't build LtHashTest.cpp on Ubuntu 20.04

I've been building in Docker using the following:

```
➜ folly git:(main) docker run -v $(pwd):/build:delegated -it ubuntu:20.04 /bin/bash
root@9c81627c5b0d:/build# apt install python3 ca-certificates
root@9c81627c5b0d:/build# ./build/fbcode_builder/getdeps.py install-system-deps --recursive
root@9c81627c5b0d:/build# apt-get install \
g++ \
cmake \
libboost-all-dev \
libevent-dev \
libdouble-conversion-dev \
libgoogle-glog-dev \
libgflags-dev \
libiberty-dev \
liblz4-dev \
liblzma-dev \
libsnappy-dev \
make \
zlib1g-dev \
binutils-dev \
libjemalloc-dev \
libssl-dev \
pkg-config \
libsodium-dev
root@9c81627c5b0d:/build# python3 ./build/fbcode_builder/getdeps.py --allow-system-packages build
```

It results in the following error. It's too big to paste here so I'm posting a [gist](https://gist.github.com/mkpankov/424b1aa82b975308040b87c313214bee).

Commenting out `LtHashTest.cpp` from `CMakeLists.txt` allows the build to complete.