In some cases, when deserializing a CXXMethodDecl of a CXXSpecializationTemplateDecl,
the call to FunctionDecl::setPure() happens before the DefinitionData member has been
populated (which appears to happen lower down in a mergeRedeclarable call), causing a
This diff fixes this by deferring the FunctionDecl::setPure() till after the DefinitionData has
been filled in.