moveAttrFromListToList only makes sense when moving an attribute to a list with
a pool that's either equivalent, or has a shorter lifetime. Therefore, using it
to move a ParsedAttr from a declarator to a declaration specifier doesn't make
sense, since the declaration specifier's pool outlives the declarator's. The
patch adds a new function, ParsedAttributes::takeOneFrom, which transfers the
attribute from one pool to another, fixing the use-after-deallocate.
rdar://49175426
Differential revision: https://reviews.llvm.org/D60101
llvm-svn: 357516
af91315668