general tree transformation. Also, implement template instantiation
for parameter packs.
In addition, introduce logic to enter the appropriate context for
subexpressions that are not potentially evaluated.
llvm-svn: 78114
transformation template (TreeTransform) that handles the
transformation and reconstruction of AST nodes. Template instantiation
for types is a (relatively small) customization of the generic tree
transformation.
llvm-svn: 78071