Make ChainedIncludesSource an ExternalSemaSource, otherwise initialization of the ASTReader is incomplete, leading to errors like not realizing std::type_info is already defined.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@128664 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed