[lld] [lld][ELF] Add --why-live flag (inspired by Mach-O) (PR #127112)

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

Thanks for working on this. I've got some subjective suggestions about the external interface.
* I recommend adding the object and section information as well as the symbol (possibly via a verbose mode). This particularly useful when there are multiple symbols and sections with the same name.
* For the root symbol, I recommend adding information about the source if its easily available. For example _start is the entry point. This could be particularly useful if a symbol is unexpectedly made live via a linker script reference.

Finally, one that you may want to exclude, is any Arm/AArch64 mapping symbol from being included in the why-live output. These often are defined at the same address as function and data symbols, but you'll almost certainly want to prefer the function and data symbol.


https://github.com/llvm/llvm-project/pull/127112