Malcolm: Usability improvements in GCC 9

David Malcolm writesabout improved diagnostics and more in the GCC 9 release."Speaking of annotations, this example shows another new GCC 9feature: diagnostics can label regions of the source code to show pertinentinformation. Here, what's most important are the types of the left-hand andright-hand sides of the '+' operator, so GCC highlights them inline. Noticehow the diagnostic also uses color to distinguish the two operands fromeach other and the operator."