Fix missing stdlib include required for abort()

Summary:
If ROCKSDB_LITE is defined, a call to abort() is introduced. This call requires stdlib.h.

Build log of unpatched 5.7.1:

http://beefy9.nyi.freebsd.org/data/110amd64-default/447974/logs/rocksdb-lite-5.7.1.log
Closes https://github.com/facebook/rocksdb/pull/2744

Reviewed By: yiwu-arbug

Differential Revision: D5632372

Pulled By: lxcode

fbshipit-source-id: b2a8e692bf14ccf1f875f3a00463e87bba310a2b

include/rocksdb/filter_policy.h

@@ -22,6 +22,7 @@
 
 #include <memory>
 #include <stdexcept>
+#include <stdlib.h>
 #include <string>
 #include <vector>