Following the build instructions and running make build_with_jit I get
curl -L https://github.com/pixie-lang/external-deps/releases/download/1.0/`uname -s`-`uname -m`.tar.bz2 > /tmp/externals.tar.bz2
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 21 0 21 0 0 3 0 --:--:-- 0:00:06 --:--:-- 5
tar -jxf /tmp/externals.tar.bz2 --strip-components=2
bzip2: (stdin) is not a bzip2 file.
tar: Child returned status 2
tar: Error is not recoverable: exiting now
make: *** [externals.fetched] Error 2
Seems that the file that it's trying to curl isn't there. (It's just {"error":"Not Found"})