-Remove Sema::ActOnCastOfParenListExpr and move most of its functionality to

 newly introduced Sema::BuildVectorLiteral.
-Make Sema::ActOnCastExpr handle a vector initializer both when the cast'ed expression
 is a ParenListExpr and when it is a ParenExpr.
-Ultimately make Sema::ActOnParenOrParenListExpr independent of what the cast type was.

llvm-svn: 134274