monotouch-test has a wildcard to automatically include new test files, but
this should not include generated files, because:
* The generated files are generated when needed, which means we can't rely on
the wildcard to trigger their generation, because the wildcard won't find
them before they exist, and as such msbuild won't detect that they're
needed.
* This means the generated files must be listed separately, but in that case
they shouldn't be found by the wildcard too, because that leads to:
/Library/Frameworks/Mono.framework/Versions/5.4.0/lib/mono/msbuild/15.0/bin/Roslyn/Microsoft.CSharp.Core.targets(84,5): error MSB3105: The item "ObjCRuntime/TrampolineTest.generated.cs" was specified more than once in the "Sources" parameter. Duplicate items are not supported by the "Sources" parameter.
So move the generated files to a different directory, so that the wildcard
doesn't find them.
Generate trampoline and registrar tests that tests if a return type requires objc_msgSend or objc_msgSend_stret.
Now it's much easier to test new return types (a single line of code), which
avoids a _lot_ of copy-pasting, and makes sure all the different variations
are tested properly.
These new tests found several bugs, which are fixed in subsequent commits.
Rolf Bjarne Kvinge