[RuntimeDyld][ELF] Fix unwanted sign extension. (#94482)

Casting the result of `Section.getAddressWithOffset()` goes wrong if we
are on a 32-bit platform whose addresses are regarded as signed; in that
case, just doing
```
(uint64_t)Section.getAddressWithOffset(...)
```
or
```
reinterpret_cast<uint64_t>(Section.getAddressWithOffset(...))
```
will result in sign-extension.

We use these expressions when constructing branch stubs, which is before
we know the final load address, so we can just switch to the
`Section.getLoadAddressWithOffset(...)` method instead.

Doing that is also more consistent, since when calculating relative
offsets for relocations, we use the load address anyway, so the code
currently only works because `Section.Address` is equal to
`Section.LoadAddress` at this point.

Fixes #94478.