[RuntimeDyld] Added support for relocation of indirect functions

[MoritzS]

Summary

In ELF, symbols of type STT_GNU_IFUNC need to be resolved by calling the
function at the symbol's address. This is implemented by adding special
stubs for all symbols of that type.

[lhames]

This is really cool.

Does the Indirect flag really need to go onto JITSymbolFlags? My mental model of ifuncs (very limited -- I haven't used them myself) is "self-updating PLT" -- its ifunc-ness is opaque to callers right?

[MoritzS]

In D105465#3653761, @lhames wrote:

Does the Indirect flag really need to go onto JITSymbolFlags? My mental model of ifuncs (very limited -- I haven't used them myself) is "self-updating PLT" -- its ifunc-ness is opaque to callers right?

Yes, you are right, ifuncs are completely opaque to callers, so we probably shouldn't add that flag. I will change that.

[MoritzS]

Removed Indirect from JITSymbolFlags

[MoritzS]

Fixed typos in comments

[MoritzS]

Rebased onto main

[MoritzS]

Rebased again because of failing tests on main