lib/cpp/test/CMakeLists.txt: Fix building with OpenBSD

OpenBSD does not have librt.
diff --git a/lib/cpp/test/CMakeLists.txt b/lib/cpp/test/CMakeLists.txt
index a73b3e6..31acf12 100644
--- a/lib/cpp/test/CMakeLists.txt
+++ b/lib/cpp/test/CMakeLists.txt
@@ -133,7 +133,7 @@
     ${Boost_LIBRARIES}
 )
 target_link_libraries(TInterruptTest thrift)
-if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT MINGW)
+if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD" AND NOT MINGW)
     target_link_libraries(TInterruptTest -lrt)
 endif ()
 add_test(NAME TInterruptTest COMMAND TInterruptTest -- "${CMAKE_CURRENT_SOURCE_DIR}/../../../test/keys")
@@ -144,7 +144,7 @@
     ${Boost_LIBRARIES}
 )
 target_link_libraries(TServerIntegrationTest thrift)
-if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT MINGW)
+if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD" AND NOT MINGW)
     target_link_libraries(TServerIntegrationTest -lrt)
 endif ()
 add_test(NAME TServerIntegrationTest COMMAND TServerIntegrationTest)
@@ -347,7 +347,7 @@
     ${Boost_LIBRARIES}
 )
 target_link_libraries(SecurityTest thrift)
-if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT MINGW)
+if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD" AND NOT MINGW)
     target_link_libraries(SecurityTest -lrt)
 endif ()
 add_test(NAME SecurityTest COMMAND SecurityTest -- "${CMAKE_CURRENT_SOURCE_DIR}/../../../test/keys")
@@ -358,7 +358,7 @@
     ${Boost_LIBRARIES}
 )
 target_link_libraries(SecurityFromBufferTest thrift)
-if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT MINGW)
+if (NOT MSVC AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD" AND NOT MINGW)
     target_link_libraries(SecurityFromBufferTest -lrt)
 endif ()
 add_test(NAME SecurityFromBufferTest COMMAND SecurityFromBufferTest -- "${CMAKE_CURRENT_SOURCE_DIR}/../../../test/keys")