CMake: Only add test/ subdirectory when it exists

[dexonsmith]

Summary

CMake: Only add test/ subdirectory when it exists

r296685 started adding the test/ subdirectory even when
LIBCXX_INCLUDE_TESTS=OFF. This is great for testing libcxx standalone,
but it also breaks the build when the test/ subdirectory is removed
(and our submission system strips all test/ directories).

This patch updates the logic to check for test/ before adding it.

rdar://problem/31931366

[EricWF]

I'm OK with this patch because it's minimally invasive. However it seems strange to support arbitrary configurations that delete random parts of the source tree.

[dexonsmith]

Thanks for being flexible; committed in r302095. Maybe longer term we could add a CMake configuration for whether to include the tests, but naming it might be hard ;).

libcxx/CMakeLists.txt

 
 if (LIBCXX_INCLUDE_BENCHMARKS)
   add_subdirectory(benchmarks)
 endif()
 
 # Create the lit.site.cfg file even when LIBCXX_INCLUDE_TESTS is OFF or
 # LLVM_FOUND is OFF. This allows users to run the tests manually using
 # LIT without requiring a full LLVM checkout.
+#
+# However, since some submission systems strip test/ subdirectories, check for
+# it before adding it.
+if(IS_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/test")
   add_subdirectory(test)
+endif()
 if (LIBCXX_INCLUDE_TESTS)
   add_subdirectory(lib/abi)
 endif()
 
 if (LIBCXX_INCLUDE_DOCS)
   add_subdirectory(docs)
 endif()