Store the type ID for __builtin_va_list in the PCH file, so that the

Store the type ID for __builtin_va_list in the PCH file, so that the
AST context's __builtin_va_list type will be set when the PCH file is
loaded. This fixes the crash when CodeGen'ing a va_arg expression
pulled in from a PCH file.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@69421 91177308-0d34-0410-b5e6-96231b3b80d8