Like the VarDecl that gets its type updated based on an init-list, this
patch corrects the MaterializeTemporaryExpr's type to make sure it isn't
creating an incomplete type, which leads to a handful of CodeGen crashes
(see PR 47636).
Based on @rsmith 's comments on D88236
Differential Revision: https://reviews.llvm.org/D88298
Erich Keane