Objective-C fast enumeration loop variables are not retained in ARC, but

they should still be officially __strong for the purposes of errors, 
block capture, etc.  Make a new bit on variables, isARCPseudoStrong(),
and set this for 'self' and these enumeration-loop variables.  Change
the code that was looking for the old patterns to look for this bit,
and change IR generation to find this bit and treat the resulting         
variable as __unsafe_unretained for the purposes of init/destroy in
the two places it can come up.

llvm-svn: 133243