Help the build system find system RocksDB.

Taken from this upstream commit:
https://github.com/ceph/ceph/commit/2ac26bd0e01fd6c82bd59936cf25c25173f7775a

diff --git a/cmake/modules/Findrocksdb.cmake b/cmake/modules/Findrocksdb.cmake
index f8369f73fc..5926647348 100644
--- a/cmake/modules/Findrocksdb.cmake
+++ b/cmake/modules/Findrocksdb.cmake
@@ -15,11 +15,11 @@ find_library(ROCKSDB_LIBRARIES rocksdb)
 
 if(ROCKSDB_INCLUDE_DIR AND EXISTS "${ROCKSDB_INCLUDE_DIR}/rocksdb/version.h")
   foreach(ver "MAJOR" "MINOR" "PATCH")
-    file(STRINGS "${ROCKSDB_INCLUDE_DIR}/version.h" ROCKSDB_VER_${ver}_LINE
+    file(STRINGS "${ROCKSDB_INCLUDE_DIR}/rocksdb/version.h" ROCKSDB_VER_${ver}_LINE
       REGEX "^#define[ \t]+ROCKSDB_${ver}[ \t]+[0-9]+$")
     string(REGEX REPLACE "^#define[ \t]+ROCKSDB_${ver}[ \t]+([0-9]+)$"
-      "\\1" ROCKSDB_VERSION_${ver} "${ROCKDB_VER_${ver}_LINE}")
-    unset(${ROCKDB_VER_${ver}_LINE})
+      "\\1" ROCKSDB_VERSION_${ver} "${ROCKSDB_VER_${ver}_LINE}")
+    unset(${ROCKSDB_VER_${ver}_LINE})
   endforeach()
   set(ROCKSDB_VERSION_STRING
     "${ROCKSDB_VERSION_MAJOR}.${ROCKSDB_VERSION_MINOR}.${ROCKSDB_VERSION_PATCH}")
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<div class='path'>path: <a href='/guix/log/?id=9a86e2e97fd91003ee089dc0fed35d848e84d0f1'>root</a>/<a href='/guix/log/tests?id=9a86e2e97fd91003ee089dc0fed35d848e84d0f1'>tests</a>/<a href='/guix/log/tests/ui.scm?id=9a86e2e97fd91003ee089dc0fed35d848e84d0f1'>ui.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/ui.scm?id=9a86e2e97fd91003ee089dc0fed35d848e84d0f1&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-12-13 17:46:39 +0100'>2022-12-13</span></td><td><a href='/guix/commit/tests/ui.scm?id=bbcd06e56c06376e640a7ac81a7109e7135a20f2'>ui: Take package upstream name into account when searching.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/ui.scm (%package-metrics): Add PACKAGE-UPSTREAM-NAME*.
* tests/ui.scm ("package-relevance and upstream name"): New test.

Co-authored-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Lars-Dominik Braun</td></tr>
<tr><td><span title='2022-06-16 23:57:41 +0200'>2022-06-16</span></td><td><a href='/guix/commit/tests/ui.scm?id=c8803d89fe531a1ff0de8ccdbc77c86249d5e778'>ui: Improve pager selection logic when less is not installed.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/ui.scm (find-available-pager): New procedure.
(call-with-paginated-output-port): Use it.
* guix/utils.scm (call-with-environment-variables): Allow clearing of
specified environment variables.
* tests/ui.scm (make-empty-file, assert-equals-find-available-pager):
New procedures.
("find-available-pager, GUIX_PAGER takes precedence")
("find-available-pager, PAGER takes precedence")
("find-available-pager, 'less' takes precedence")
("find-available-pager, 'more' takes precedence")
("find-available-pager, no pager"): New tests.

Co-authored-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Taiju HIGASHI</td></tr>