This patch implements objective-c's 'SEL' type as a built-in

type and fixes a long-standing code gen. crash reported in
at least two PRs and a radar. (radar 7405040 and pr5025). 
There are couple of remaining issues that I would like for
Ted. and Doug to look at:

Ted, please look at failure in Analysis/MissingDealloc.m.
I have temporarily added an expected-warning to make the
test pass. This tests has a declaration of 'SEL' type which
may not co-exist with the new changes.

Doug, please look at a FIXME in PCHWriter.cpp/PCHReader.cpp.
I think the changes which I have ifdef'ed out are correct. They
need be considered for in a few Indexer/PCH test cases.

llvm-svn: 89561