Updated serialization test code in the driver to test serialization of
these types.

llvm-svn: 43266

Silenced some VC++ warnings.
Had to rephrase a partial specialization of the IntrospectionTrait struct in SerializationTest.cpp, please review.
Added a compiler specific workaround in IdentifierTable.h. Is that the way to fix this kind of issues?

llvm-svn: 43074

llvm-svn: 43057

serialization logic as well as driver code is now in
Driver/SerializationTest.cpp.  The status of this code is that it
should be used by no clients.

Added --test-pickling option to driver to run the serialization code.

Modified IdentifierInfo and IdentifierTable to have friend classes
that permit object serialization.  Such friendship may not be needed
in the final design.

llvm-svn: 43052