Sema: process non-inheritable attributes on function declarations early

This allows us to simplify the handling for the overloadable attribute,
removing a number of FIXMEs.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@123961 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed