Re-enable io tests
Summary:
Looks like some tests for the `io` directory were left behind when they were moved out of experimental. Re-enabled them in the new location, except for the compression test because it takes a lot longer. It's still built and can be executed manually.
Also added some preprocessor guards around compression codecs that might not be compiled in (and therefore fail during test SetUp).
Depends on #547 because the path to gtest appears in the new Makefile.am's `CPPFLAGS`.
Closes https://github.com/facebook/folly/pull/550
Reviewed By: yfeldblum
Differential Revision:
D4631244
Pulled By: Orvid
fbshipit-source-id:
496b2c272e4f7293822f159776a02f7dd0c9e04d