[LIT] Add support for UNSUPPORTED tag to TestRunner.parseIntegratedTestScript

Summary:
This patch gives me just enough to leverage the existing functionality in `TestRunner` for use in `libc++` and `libc++abi` .

It does the following:
* Adds the `UNSUPPORTED` tag to `TestRunner.parseIntegratedTestScript`.
* Allows `parseIntegratedTestScript` to return an empty script if a script is not required by the caller.



Reviewers: ddunbar, EricWF

Reviewed By: EricWF

Subscribers: cfe-commits, llvm-commits

Differential Revision: http://reviews.llvm.org/D6589

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223915 91177308-0d34-0410-b5e6-96231b3b80d8

utils/lit/lit/util.py

@@ -7,6 +7,15 @@ import signal
 import subprocess
 import sys
 
+def to_bytes(str):
+    # Encode to UTF-8 to get binary data.
+    return str.encode('utf-8')
+
+def to_string(bytes):
+    if isinstance(bytes, str):
+        return bytes
+    return to_bytes(bytes)
+
 def detectCPUs():
     """
     Detects the number of CPUs on a system. Cribbed from pp.
@@ -156,11 +165,6 @@ def executeCommand(command, cwd=None, env=None):
     if exitCode == -signal.SIGINT:
         raise KeyboardInterrupt
 
-    def to_string(bytes):
-        if isinstance(bytes, str):
-            return bytes
-        return bytes.encode('utf-8')
-
     # Ensure the resulting output is always of string type.
     try:
         out = to_string(out.decode('utf-8'))