Author: Kefu Chai <tchaikov@gmail.com>
Description: cmake/modules/BuildRocksDB.cmake: use string(APPEND ..) when appropriate
 less repeatings this way.
 .
 https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/W5QEP4PM6G6L62W5PNJMGXU4Y26437XL/

diff -Naurp ceph.orig/cmake/modules/BuildRocksDB.cmake ceph/cmake/modules/BuildRocksDB.cmake
--- ceph.orig/cmake/modules/BuildRocksDB.cmake
+++ ceph/cmake/modules/BuildRocksDB.cmake
@@ -57,11 +57,11 @@ function(build_rocksdb)
   include(CheckCXXCompilerFlag)
   check_cxx_compiler_flag("-Wno-deprecated-copy" HAS_WARNING_DEPRECATED_COPY)
   if(HAS_WARNING_DEPRECATED_COPY)
-    set(rocksdb_CXX_FLAGS -Wno-deprecated-copy)
+    string(APPEND rocksdb_CXX_FLAGS " -Wno-deprecated-copy")
   endif()
   check_cxx_compiler_flag("-Wno-pessimizing-move" HAS_WARNING_PESSIMIZING_MOVE)
   if(HAS_WARNING_PESSIMIZING_MOVE)
-    set(rocksdb_CXX_FLAGS "${rocksdb_CXX_FLAGS} -Wno-pessimizing-move")
+    string(APPEND rocksdb_CXX_FLAGS " -Wno-pessimizing-move")
   endif()
   if(rocksdb_CXX_FLAGS)
     list(APPEND rocksdb_CMAKE_ARGS -DCMAKE_CXX_FLAGS='${rocksdb_CXX_FLAGS}')