Fix building async_io_test (#1313)

Summary:
Since 60da8ef5, typed tests have been moved to a separate unit (`AsyncBaseTestLib`), which is not the part of `folly` or `folly_test_support`.

This commit adds `AsyncBaseTestLib` to `async_io_test`'s sources.

Alternatively, the test lib could be added to `folly_test_support` with an additional check on `LIBAIO_FOUND`, but `AsyncBaseTestLib` has a specific `TemporaryFile` implementation that conflicts with the one in `experimental/TestUtil.h`.
Pull Request resolved: https://github.com/facebook/folly/pull/1313

Reviewed By: simpkins

Differential Revision: D19648091

Pulled By: yfeldblum

fbshipit-source-id: 27881b464dc3c84aa20ffee1ffd3320e0a67eb27

CMakeLists.txt

@@ -915,7 +915,7 @@ if (BUILD_TESTS)
   if (${LIBAIO_FOUND})
     folly_define_tests(
       DIRECTORY experimental/io/test/
-        TEST async_io_test SOURCES AsyncIOTest.cpp
+        TEST async_io_test SOURCES AsyncIOTest.cpp AsyncBaseTestLib.cpp
     )
   endif()