Fixes an instance method meta-data generation bug in

Fixes an instance method meta-data generation bug in
ObjC NeXt runtime where method pointer registered in
metadata belongs to an unrelated method. Ast part of this fix,
I turned at @end missing warning (for class
implementations) into an error as we can never
be sure that meta-data being generated is correct.
// rdar://9072317

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@130019 91177308-0d34-0410-b5e6-96231b3b80d8