Tests started to fail on macOS on the most recent master

[pepyakin]

745d606 made tests on my local macOS machine to fail.

$ sw_vers

ProductName:    Mac OS X
ProductVersion:    10.12.6
BuildVersion:    16G29

$ clang --version

Apple LLVM version 8.1.0 (clang-802.0.42)
Target: x86_64-apple-darwin16.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

Here is build log.

[emilio]

Hmm, right. Now we have the problem that symbols on those platforms are actually different. :(

[emilio]

So, options I'm seeing:

• Run tests with a linux64 target by default. That's easiest, but likely misses support? Also, test_expectations probably won't build.

• Reverting that for now, or hiding it behind an option. We really want proper unmangled symbols instead of tracking down all the platforms it affects.

• Add tests per-platform, and run them with different --target values.

• Make the runner ignore trivial link_name differences?

[liranringel]

@emilio As I understand it, the functionality is correct, but the tests need refactor.
That fix is something I've been waiting for some time (for the ipconfig and trust-dns crates), and it's unfortunate if it won't land on version 0.31.

I prefer the option to ignore link_name differences. We probably don't want to make different expectation file for every platform, and I believe we can trust clang to produce the correct mangling.

[emilio]

Right, I agree, and I think reverting would be really unfortunate. We probably just need an easy way to update tests for all platforms (can be done with --target) and build tests for the correct platform.

[fitzgen]

Run tests with a linux64 target by default. That's easiest, but likely misses support? Also, test_expectations probably won't build.

Inserting an implicit --target if there isn't one explicitly specified is probably easiest.

Note that the test expectations don't actually call any of the declared functions, so we won't get link errors (otherwise, we would get them now).