IRgen/Obj-C: Emit CFStrings and NSStrings with the alignment of the char type,

there is no reason to align them higher.
 - This roughly matches llvm-gcc's r126913.
 - It is an open question whether or not we should do this for cstring's in
   general (code size vs optimization potential), for now we just match llvm-gcc
   until someone wants to run some experiments.

llvm-svn: 129410