Fix compatibility with newer versions of RocksDB.

Adapted from this upstream patch, with some additional changes for 12.2:
https://github.com/ceph/ceph/commit/9d73a7121fdb1ae87cb1aa6f7d9d7a13f329ae68

diff --git a/src/kv/RocksDBStore.cc b/src/kv/RocksDBStore.cc
index 8660afe1886d..bc0de79e23cb 100644
--- a/src/kv/RocksDBStore.cc
+++ b/src/kv/RocksDBStore.cc
@@ -505,7 +505,7 @@
   // considering performance overhead, default is disabled
   if (g_conf->rocksdb_perf) {
     rocksdb::SetPerfLevel(rocksdb::PerfLevel::kEnableTimeExceptForMutex);
-    rocksdb::perf_context.Reset();
+    rocksdb::get_perf_context()->Reset();
   }
 
   RocksDBTransactionImpl * _t =
@@ -532,13 +532,13 @@
     utime_t write_wal_time;
     utime_t write_pre_and_post_process_time;
     write_wal_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_wal_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_wal_time)/1000000000);
     write_memtable_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_memtable_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_memtable_time)/1000000000);
     write_delay_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_delay_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_delay_time)/1000000000);
     write_pre_and_post_process_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_pre_and_post_process_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_pre_and_post_process_time)/1000000000);
     logger->tinc(l_rocksdb_write_memtable_time, write_memtable_time);
     logger->tinc(l_rocksdb_write_delay_time, write_delay_time);
     logger->tinc(l_rocksdb_write_wal_time, write_wal_time);
@@ -558,7 +558,7 @@
   // considering performance overhead, default is disabled
   if (g_conf->rocksdb_perf) {
     rocksdb::SetPerfLevel(rocksdb::PerfLevel::kEnableTimeExceptForMutex);
-    rocksdb::perf_context.Reset();
+    rocksdb::get_perf_context()->Reset();
   }
 
   RocksDBTransactionImpl * _t =
@@ -586,13 +586,13 @@
     utime_t write_wal_time;
     utime_t write_pre_and_post_process_time;
     write_wal_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_wal_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_wal_time)/1000000000);
     write_memtable_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_memtable_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_memtable_time)/1000000000);
     write_delay_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_delay_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_delay_time)/1000000000);
     write_pre_and_post_process_time.set_from_double(
-	static_cast<double>(rocksdb::perf_context.write_pre_and_post_process_time)/1000000000);
+	static_cast<double>(rocksdb::get_perf_context()->write_pre_and_post_process_time)/1000000000);
     logger->tinc(l_rocksdb_write_memtable_time, write_memtable_time);
     logger->tinc(l_rocksdb_write_delay_time, write_delay_time);
     logger->tinc(l_rocksdb_write_wal_time, write_wal_time);
='/guix/commit/build-aux/check-final-inputs-self-contained.scm?id=4debffadb7e166e34fb2ef00e75c4b73977ede15'>maint: Adjust 'check-final-inputs-self-contained' for glibc:static.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-05-08 16:29:23 +0200'>2017-05-08</span></td><td><a href='/guix/commit/build-aux/check-final-inputs-self-contained.scm?id=c8ba269c26c85c5eae6bf5be9add881111c18a22'>maint: Use 'G_' in build-aux/ scripts.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-12-18 12:37:26 +0100'>2016-12-18</span></td><td><a href='/guix/commit/build-aux/check-final-inputs-self-contained.scm?id=8a4c98889270c163581231692fef64d9433b101f'>build: check-final-inputs-self-contained has an exception for 'bash:include'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-03-03 23:54:36 +0100'>2016-03-03</span></td><td><a href='/guix/commit/build-aux/check-final-inputs-self-contained.scm?id=5c7e1a32709365949ebc952109621bc770d44664'>build: Use (guix grafts) as needed.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>