rocksdb: build with ppc64

changes included:

- cmake: check -momit-leaf-frame-pointer before using it
- util/thread_local.h: silence a clang-build warning

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/src/rocksdb b/src/rocksdb
index a0deec960f3a8190831c673e5ba998fe6fb7ea90..a9b0a54f4925a5a48c70fc19257af988acebcea9 160000 (submodule)
--- a/src/rocksdb
+++ b/src/rocksdb
@@ -1 +1 @@
-Subproject commit a0deec960f3a8190831c673e5ba998fe6fb7ea90
+Subproject commit a9b0a54f4925a5a48c70fc19257af988acebcea9