Improve name mangling for instantiation-dependent types that are not

dependent. This covers an odd class of types such as

  int (&)[sizeof(sizeof(T() + T()))];

which involve template parameters but, because of some trick typically
involving a form of expression that is never type-dependent, resolve
down to a non-dependent type. Such types need to be mangled
essentially as they were written in the source code (involving
template parameters), rather than via their canonical type.

In general, instantiation-dependent types should be mangled as
they were written in the source. However, since we can't do that now
without non-trivial refactoring of the AST (see the new FIXME), I've
gone for this partial solution: only use the as-written-in-the-source
mangling for these strange types that are instantiation-dependent but
not dependent. This provides better compatibility with previous
incarnations of Clang and with GCC. In the future, we'd like to get
this right.

Fixes <rdar://problem/9663282>.

llvm-svn: 134984