Sema-based fix for PR2334. The issue is that even if the two sides of

the condidtional have compatible types, they are not necessarily the 
same type.  Therefore, we cast to the composite type.  As a hack, for 
the moment we assume that the composite type is the type of the 
left-hand expression; this isn't correct, but it's good enough for most 
purposes.

llvm-svn: 51202