This patch implements as much of the narrowing conversion error specified by

[dcl.init.list] as is possible without generalized initializer lists or full
constant expression support, and adds a c++0x-compat warning in C++98 mode.

The FixIt currently uses a typedef's basename without qualification, which is
likely to be incorrect on some code.  If it's incorrect on too much code, we
should write a function to get the string that refers to a type from a
particular context.

The warning is currently off by default. I'll fix LLVM and clang before turning
it on.

llvm-svn: 136181