Tweaks to Objective-C metadata (32 & 64-bit) to match llvm-gcc.

 - Set alignment on property lists.
 - 32-bit:
   o Set section on property lists.
   o Fix section name for category class methods.
   o Fix symbol name for property lists.
   o Fix section name for class method.
   o Set alignment and section on class extension structure.
   o Set alignment on a number of things: instance variables, methods,
   method descriptions, the symbols structure.
 - 64-bit:
   o Fix section flags for protocol list.

I doubt most of these were problems in practice, but it is nice to
match llvm-gcc.

llvm-svn: 69132