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

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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@129410 91177308-0d34-0410-b5e6-96231b3b80d8