Failing to build on Mac OS X Catalina

I'm struggling to build the extension on Mac OS X. Using the following steps from [the docs](https://pgxn.org/dist/hll/#Build):

```
git clone git@github.com:citusdata/postgresql-hll.git
cd postgresql-hll
make CC=gcc CXX=gcc
```

I keep getting the following error / output:

> gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -Wno-unused-command-line-argument -mmacosx-version-min=10.12 -bundle -multiply_defined suppress -o hll.so src/hll.o src/MurmurHash3.o -L/Applications/Postgres.app/Contents/Versions/12/lib -L/Applications/Postgres.app/Contents/Versions/12/lib -L/Applications/Postgres.app/Contents/Versions/12/lib -Wl,-dead_strip_dylibs -bundle_loader /Applications/Postgres.app/Contents/Versions/12/bin/postgres -lstdc++
> Undefined symbols for architecture x86_64:
> "_AllocSetContextCreate", referenced from:
> _setup_multiset in hll.o
> "_heap_open", referenced from:
> _get_extension_schema in hll.o
> ld: symbol(s) not found for architecture x86_64
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
> make: *** [hll.so] Error 1

**Environment**

- Postgressapp Version 2.3.5 (80)
- PostgreSQL v12
- Mac OS Catalina (v10.15.6)

Is this a known issue? Let me know if I can provide any more information.

Thanks in advance!