Treat module headers wrapped by our builtin headers as implicitly being textual

Treat module headers wrapped by our builtin headers as implicitly being textual
headers. We previously got this check backwards and treated the wrapper header
as being textual.

This is important because our wrapper headers sometimes inject macros into the
system headers that they #include_next, and sometimes replace them entirely.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@285152 91177308-0d34-0410-b5e6-96231b3b80d8