Instead, we now have a looser helper called `checkContains(...)`
that will match on any occurrence similarly to `std.mem.indexOf()`.
While at it, I have cleaned up other combinators to make the entire
API more consistent, and so:
* `checkStart(phrase)` is now `checkStart()` followed by
`checkExact(phrase)`
* `checkNext(phrase)` if matching exactly is now `checkExact(phrase)`
* `checkNext(phrase)` if matching loosely is now `checkContains(phrase)`
* `checkNext(phrase)` if matching exactly with var extractors is now
`checkExtract(phrase)`
Finally, `ElfDumper` is now dumping contents of `.symtab` and `.dynsym`
symbol tables. I have also removed dumping of symtabs as optional - they
are now always dumped which cleaned up the implementation even more.
Also clean up parsing of linker args - reuse `ArgsIterator`.
In MachO, ensure we add every symbol marked with `-u` as undefined
before proceeding with symbol resolution. Additionally, ensure those
symbols are never garbage collected.
MachO entry_in_dylib test: pass `-u _my_main` when linking executable
so that it is not incorrectly garbage collected by the linker.
