Fix PCH deserialization bug with local static symbols being treated as local extern.

This triggered a miscompilation of code using Boost's function_template.hpp
when it was included inside a PCH file.  A local static within
that header would be treated as local extern, resulting in the wrong
mangling.  This only occurred during PCH deserialization.

Fixes <rdar://problem/15975816> and <rdar://problem/15926311>.