Fix size calculation from r339380

r339380 changed the trailing types of ParsedAttr to use llvm::TrailingObjects.
However, it did not copy over one of the size attributes, causing a too
small allocation for this object.  The error was detected with
AddressSanitizer use-after-poison


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@339409 91177308-0d34-0410-b5e6-96231b3b80d8