Fix missing builtin identifier infos with PCH+modules
Use the *current* state of "is-moduleness" rather than the state at
serialization time so that if we read a builtin identifier from a module
that wasn't "interesting" to that module, we will still write it out to
a PCH that imports that module.
Otherwise, we would get mysterious "unknown builtin" errors when using
PCH+modules.
rdar://problem/
23287656
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@251565
91177308-0d34-0410-b5e6-
96231b3b80d8