Implement the __builtin_call_with_static_chain GNU extension.

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