[clang] [DebugInfo] Add flag to only emit referenced member functions (PR #87018)

[Reid Kleckner via cfe-commits]

rnk wrote:

To restate the finding, 29% of .debug_info is describing class methods, at least in Clang.

I think this is a useful mode, and we should land it as is. There are many users up against the scaling limits of debug info size, and it's helpful to have this as an option for experimentation in the field. We should document somewhere that this flat is known to be incompatible with some debugger features.

https://github.com/llvm/llvm-project/pull/87018