disable function_scheduler_test on cmake-based builds

Summary:
Unfortunately it looks like D6880256 was not sufficient to make
function_scheduler_test pass reliably on Travis CI builds.  This just disables
function_scheduler_test on open source CMake-based builds for now.

Ideally in the future we should try to convert most of the function scheduler
to use proper synchronization mechanisms (like folly::Baton) for synchronizing
between threads, rather than sleeping and expecting the other thread to have
completed its work before we wake up.

Reviewed By: yfeldblum

Differential Revision: D6891889

fbshipit-source-id: 9ee98f5807e1d90f083bd942ba98df6fad656ba6

CMakeLists.txt

@@ -415,7 +415,9 @@ if (BUILD_TESTS)
       TEST dynamic_parser_test SOURCES DynamicParserTest.cpp
       TEST eliasfano_test SOURCES EliasFanoCodingTest.cpp
       TEST event_count_test SOURCES EventCountTest.cpp
-      TEST function_scheduler_test SOURCES FunctionSchedulerTest.cpp
+      # FunctionSchedulerTest has a lot of timing-dependent checks,
+      # and tends to fail on heavily loaded systems.
+      TEST function_scheduler_test BROKEN SOURCES FunctionSchedulerTest.cpp
       TEST future_dag_test SOURCES FutureDAGTest.cpp
       TEST json_schema_test SOURCES JSONSchemaTest.cpp
       TEST lock_free_ring_buffer_test SOURCES LockFreeRingBufferTest.cpp