Move "Eliminate Available Externally" immediately after the inliner

This pass is supposed to reduce the size of the IR for compile time
purpose. We should run it ASAP, except when we prepare for LTO or
ThinLTO, and we want to keep them available for link-time inline.

Differential Revision: http://reviews.llvm.org/D19813

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 268394