Frontend: Canonicalize to native paths when dumping module dependencies

Mixed path separators (ie, both / and \\) can mess up the sort order
of the VFS map when dumping module dependencies, as was recently
exposed by r224055 and papered over in r224145. Instead, we should
simply use native paths for consistency.

This also adds a TODO to add handling of .. in paths. There was some
code for this before r224055, but it was untested and probably broken.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224164 91177308-0d34-0410-b5e6-96231b3b80d8
Implement the __builtin_call_with_static_chain GNU extension.

The extension has the following syntax:

  __builtin_call_with_static_chain(Call, Chain)
  where Call must be a function call expression and Chain must be of pointer type

This extension performs a function call Call with a static chain pointer
Chain passed to the callee in a designated register. This is useful for
calling foreign language functions whose ABI uses static chain pointers
(e.g. to implement closures).

Differential Revision: http://reviews.llvm.org/D6332

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224167 91177308-0d34-0410-b5e6-96231b3b80d8