runtime: tidy Windows callback test
This simplifies the systematic test of Windows callbacks with
different signatures and prepares it for expanded coverage of function
signatures.
It now returns a result from the Go function and threads it back
through C. This simplifies things, but also previously the code could
have succeeded by simply not calling the callbacks at all (though
other tests would have caught that).
It bundles together the C function description and the Go function
it's intended to call. Now the test source generation and the test
running both loop over a single slice of test functions.
Since the C function and Go function are now bundled, it generates the
C function by reflectively inspecting the signature of the Go
function. For the moment, we keep the same test suite, which is
entirely functions with "uintptr" arguments, but we'll expand this
shortly.
It now use sub-tests. This way tests automatically get useful
diagnostic labels in failures and the tests don't have to catch panics
on their own.
It eliminates the DLL function argument. I honestly couldn't figure
out what the point of this was, and it added what appeared to be an
unnecessary loop level to the tests.
Change-Id: I120dfd4785057cc2c392bd2c821302f276bd128e
Reviewed-on: https://go-review.googlesource.com/c/go/+/263270
Trust: Austin Clements <austin@google.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>