[Gold] Skip linking when output file is newer than all inputs?

[Niklas Hambüchen]

> If I understand you correctly, that's what the make program is for.  I
> don't think gold needs to have the same functionality.

That's not what I meant, in a Makefile you usually have no way to
actually depend on a big number of ld inputs - for example when they are
in system paths and you reference them by name (e.g. -l...); the logic
to select from these paths is inside the linker program.