cmake: mark the compression tests as slow

Summary:
The compression test code has a large number of parameterized tests that run
with a large number of parameter combinations.  These tests take many minutes
to run.

Reviewed By: meyering

Differential Revision: D6745364

fbshipit-source-id: dac5d5eb4a786da7be453742fac5f92a9740e468

CMakeLists.txt

@@ -351,7 +351,7 @@ if (BUILD_TESTS)
       TEST chrono_conv_test SOURCES ConvTest.cpp
 
     DIRECTORY compression/test/
-      TEST compression_test SOURCES CompressionTest.cpp
+      TEST compression_test SLOW SOURCES CompressionTest.cpp
 
     DIRECTORY container/test/
       TEST access_test SOURCES AccessTest.cpp