Correctly remove OptimizeForSize from functions marked OptimizeNone.
This allows using __attribute__((optnone)) and the -Os/-Oz options.
Fixes PR21604.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@222683 91177308-0d34-0410-b5e6-96231b3b80d8