Refactoring in preparation for having multiple

calls to the FindExternalVisibleDecls function.

FindExternalVisibleDecls was recording whether
it had found generic function symbols in variables
that were local to the function.  Now, however,
multiple calls occur in response to one request
from Clang, since we may be searching across
namespaces.  To support that, I moved the local
variables into a bitfield in NameSearchContext.

llvm-svn: 141808