Pinned llvm version to one that compiles correctly with python 2.7 (#3137)

llvmlite is now pinned to 0.31.0. 

Co-authored-by: Hoyt Koepke <[email protected]>

Author: Hoyt Koepke

src/python/setup.py

@@ -136,6 +136,9 @@ def run(self):
         "scipy >= 1.1.0",
         "six >= 1.10.0",
     ]
+    if sys.version_info[0] == 2:
+        install_requires.append("llvmlite == 0.31.0")
+
     if sys.platform == "darwin":
         install_requires.append("tensorflow >= 2.0.0")
     else: