Avoid abort on "memory read -s N" for N=3,5,6,7

We cannot use "GetMaxU64Bitfield" for non-power-of-two sizes, so just use
the same code that handles N > 8 for these.

Review: http://llvm-reviews.chandlerc.com/D1699
ObjectiveC modern translator: Provide proper cast of
the ObjectiveC object of an @synchronized statement.
// rdar://14993814