Add artifact suffix to shared library (#7755)

Summary:
On Unix systems, `ARTIFACT_SUFFIX` was added to the static library `librocksdb.a` but not the shared library `librocksdb.so`

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7755

Reviewed By: ajkr

Differential Revision: D25988550

Pulled By: jay-zhuang

fbshipit-source-id: 8079f26802ac937d5a75cbd6d3c0544094df1b11

CMakeLists.txt

@@ -945,7 +945,7 @@ if(ROCKSDB_BUILD_SHARED)
                           LINKER_LANGUAGE CXX
                           VERSION ${rocksdb_VERSION}
                           SOVERSION ${rocksdb_VERSION_MAJOR}
-                          OUTPUT_NAME "rocksdb")
+                          OUTPUT_NAME "rocksdb${ARTIFACT_SUFFIX}")
   endif()
 endif()