Fixed a bug where we were tail calling objc_autorelease causing an object to...

Fixed a bug where we were tail calling objc_autorelease causing an object to not be placed into an autorelease pool.

The reason that this occurs is that tail calling objc_autorelease eventually
tail calls -[NSObject autorelease] which supports fast autorelease. This can
cause us to violate the semantic gaurantees of __autoreleasing variables that
assignment to an __autoreleasing variables always yields an object that is
placed into the innermost autorelease pool.

The fix included in this patch works by:

1. In the peephole optimization function OptimizeIndividualFunctions, always
remove tail call from objc_autorelease.
2. Whenever we convert to/from an objc_autorelease, set/unset the tail call
keyword as appropriate.

*NOTE* I also handled the case where objc_autorelease is converted in
OptimizeReturns to an autoreleaseRV which still violates the ARC semantics. I
will be removing that in a later patch and I wanted to make sure that the tree
is in a consistent state vis-a-vis ARC always.

Additionally some test cases are provided and all tests that have tail call marked
objc_autorelease keywords have been modified so that tail call has been removed.

*NOTE* One test fails due to a separate bug that I am going to commit soon. Thus
I marked the check line TMP: instead of CHECK: so make check does not fail.

llvm-svn: 172287