Update swift-rpathize.py to work with Python 3.8 and Python 2.7 (#34332)

* Update swift-rpathize.py to work with Python 3.8 and Python 2.7

In Python 2, str() is also a kind of bytes blob
In Python 3, str() is a Unicode string that's unrelated

* Avoid `l` as a variable name

Python-lint correctly warns about single-character variables that can be confused with numbers

Author: tbkka

utils/swift-rpathize.py

@@ -64,7 +64,8 @@ def rpathize(filename):
 
     # Build a command to invoke install_name_tool.
     command = ['install_name_tool']
-    for line in dylibsOutput.splitlines():
+    for binaryline in dylibsOutput.splitlines():
+        line = binaryline.decode("utf-8", "strict")
         match = dylib_regex.match(line)
         if match:
             command.append('-change')