[PATCH] [libcxx] Add better support for custom test runners.

[Eric Fiselier]

================
Comment at: test/lit.cfg:204
@@ -184,3 +203,3 @@
                 try:
-                    os.remove(exec_path)
+                    self._clean(exec_path)
                 except:
----------------
danalbert wrote:
> EricWF wrote:
> > `exec_path` is always created so it should always be removed.  If creating the file doesn't belong to a customization point then neither should cleaning it up. 
> > 
> > Small nit: Will there ever be a case we want `_clean(...)` to throw? Should exception handling be the responsibility of `_clean(...)`?
> The build step is the one that creates the file, and that _is_ customizable. Remote test executors need to customize the cleanup step because they need to remove the output from both the compilation location and the run location.
> 
> Yeah, I'm thinking `_clean()` worries about the exceptions, since the action taken might vary based on the internals (adb fails often, so probably just retry, whereas `os.remove()` will probably only fail for bad permissions, in which case just ignore).
Isn't the file created by `exec_file = tempfile.NamedTemporaryFile(suffix="exe", delete=False)` on line 170? The `_build` step just overwrites it.

http://reviews.llvm.org/D6373