CMakeLists: Add Clang's Specific WShadow Diagnostics

[mitaclaw]

For Clang parity with GCC. GCC is justified in detecting this, as it is technically correct when using decltype, but I believe it would be better to disable the warning if it were an option, hence my comment.

[mitaclaw]

This change is motivated by #12610 being necessary after Clang failed to notify me of these GCC warnings.

[mitaclaw]

Clang also has -Wshadow-field-in-constructor, another kind of shadowing Clang does not detect by default which GCC detects as part of its -Wshadow option. Would it be worth enabling that as well for parity, seeing as we already avoid it in many places?

[AdmiralCurtiss]

Yes, please add -Wshadow-field-in-constructor. I'd also remove the comment, though I get where you're coming from.

[mitaclaw]

Looking again at Clang's documentation, there is also -WShadow-field to catch members shadowed during inheritance.
https://releases.llvm.org/5.0.0/tools/clang/docs/DiagnosticsReference.html#wshadow-field
Enabling this, it doesn't seem to happen anywhere in Dolphin's codebase. Is it worth adding as well?

[AdmiralCurtiss]

Oh, sorry didn't see that comment. If you want, but it seems pretty unlikely to be a problem.