New folly_test_util library for functions used by other projects (#1071)

Summary:
LogDevice uses DeterministicSchedule and JsonTestUtil from Folly make
these available in the installed library targets so that LogDevice can
compile against installed folly rather than referencing sources
directly.
Pull Request resolved: https://github.com/facebook/folly/pull/1071

Reviewed By: yfeldblum

Differential Revision: D14531954

Pulled By: calebmarchent

fbshipit-source-id: 9bd343210451ad6b2e171c6ddddb7d8677fa6290

CMakeLists.txt

@@ -325,6 +325,19 @@ apply_folly_compile_options_to_target(folly)
 
 target_link_libraries(folly PUBLIC folly_deps)
 
+# Test utilities exported for use by downstream projects
+add_library(folly_test_util
+  ${FOLLY_DIR}/test/DeterministicSchedule.cpp
+  ${FOLLY_DIR}/test/JsonTestUtil.cpp
+)
+target_link_libraries(folly_test_util
+  PUBLIC
+    ${BOOST_LIBRARIES}
+    folly
+    ${LIBGMOCK_LIBRARIES}
+)
+apply_folly_compile_options_to_target(folly_test_util)
+list(APPEND FOLLY_INSTALL_TARGETS folly_test_util)
 
 install(TARGETS ${FOLLY_INSTALL_TARGETS}
   EXPORT folly