Find .o files in src/Makefile for Lua 5.1.5 and 5.2.4

The Lua GitHub repository doesn't have tags for the 5.1.5 and 5.2.4
releases(see lua/lua#16 (comment)).
And the source files downloaded from https://www.lua.org/ftp have
different directory layout.

setup.py

@@ -263,6 +263,9 @@ def use_bundled_lua(path, macros):
 
     # Parse .o files from 'makefile'
     makefile = os.path.join(path, "makefile")
+    # Source code of Lua 5.1.5 and 5.2.4 are downloaded from https://www.lua.org/ftp
+    if not os.path.exists(makefile):
+        makefile = os.path.join(path, "src", "Makefile")
     match_var = re.compile(r"(CORE|AUX|LIB|ALL)_O\s*=(.*)").match
     is_indented = re.compile(r"\s+").match