When setting the globally-visible declarations for a particular

identifier, we may have a Sema object but no translation unit scope
(because parsing is finished). In this case, we still need to update
the IdResolver, which might still be used when writing a PCH
containing another PCH (without chaining). This bug manifested as a
failure with precompiled preambles.

Also, add a little environment-variable-sensitive logging for
libclang.

llvm-svn: 114774