Switch the type-trait like APIs on the AST to only check for incomplete

types after looking through arrays. Arrays with an unknown bound seem to
be specifically allowed in the library type traits in C++0x, and GCC's
builtin __is_trivial returns 'true' for the type 'int[]'. Now Clang
agrees with GCC about __is_trivial here.

Also hardens these methods against dependent types by just returning false.

llvm-svn: 130605