InterOp::Declare silent=true issue

[vgvassilev]

In the interface InterOp::Declare we have an option silent which means that even if the code does not compile we should not print an error on the screen.

Currently: https://github.com/compiler-research/CppInterOp/blob/8963daa77d3038cf35cd5d4c8d9f22fbb9e4f324/lib/Interpreter/InterOp.cpp#L2586-L2587

We handle this by turning on suppressing all diagnostics here:

https://github.com/compiler-research/CppInterOp/blob/8963daa77d3038cf35cd5d4c8d9f22fbb9e4f324/lib/Interpreter/InterOp.cpp#L2567-L2579

However, this prevents us to realize there was an error because the interpreter checks if diagnostics occurred to set the error and InterOp::Declare to return kFailure. If silent is passed we should swap the default diagnostic consumer with IgnoringDiagConsumer. However, the problem is that we should have some place to store the default and the ignoring consumer. The storing of such state is problematic for CppInterOp as we do not want many function static members but do not have a good way to store this. Perhaps the easiest would be to implement our custom clang::DiagnosticConsumer which has a flag to ignore the coming diagnostics.

[sudo-panda]

[cling]$ InterOp::Declare("int i;", true)
(unsigned long) 0
[cling]$ InterOp::Declare("int i;", true)
(unsigned long) 1
[cling]$ InterOp::Declare("integer i;", true)
(unsigned long) 1
[cling]$ InterOp::Declare("int i1;", true)
(unsigned long) 0

It works on the cling backend, so it's only a problem on clang-REPL backend