rocksdb: FreeBSD disable jemalloc search

FreeBSD's inbuilt default jemalloc means its pointless
to do a package search on it. The paths are already set
by the system defaults.

storage/rocksdb/build_rocksdb.cmake

@@ -18,17 +18,16 @@ if(WIN32)
   # include(${ROCKSDB_SOURCE_DIR}/thirdparty.inc)
 else()
   option(WITH_ROCKSDB_JEMALLOC "build RocksDB with JeMalloc" OFF)
-  if(WITH_ROCKSDB_JEMALLOC)
-    find_package(JeMalloc REQUIRED)
-    add_definitions(-DROCKSDB_JEMALLOC)
-    ADD_DEFINITIONS(-DROCKSDB_MALLOC_USABLE_SIZE)
-    include_directories(${JEMALLOC_INCLUDE_DIR})
-  endif()
   if(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
     # FreeBSD has jemaloc as default malloc
     add_definitions(-DROCKSDB_JEMALLOC)
     ADD_DEFINITIONS(-DROCKSDB_MALLOC_USABLE_SIZE)
     set(WITH_JEMALLOC ON)
+  elseif(WITH_ROCKSDB_JEMALLOC)
+    find_package(JeMalloc REQUIRED)
+    add_definitions(-DROCKSDB_JEMALLOC)
+    ADD_DEFINITIONS(-DROCKSDB_MALLOC_USABLE_SIZE)
+    include_directories(${JEMALLOC_INCLUDE_DIR})
   endif()
 endif()