Merging r182066:

------------------------------------------------------------------------
r182066 | gclayton | 2013-05-16 17:55:28 -0700 (Thu, 16 May 2013) | 5 lines

<rdar://problem/13893094>

Show variables that were in the debug info but optimized out. Also display a good error message when one of these variables get used in an expression.


------------------------------------------------------------------------

llvm-svn: 182516