Fix gcc-11 compile error (#9043)

Summary:
gcc11 added new static check.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9043

Test Plan: Added CI for gcc11 build

Reviewed By: zhichao-cao

Differential Revision: D31716005

Pulled By: jay-zhuang

fbshipit-source-id: 9f53be6f2f9e58e39b83359f6bbf66f945d57429

.circleci/config.yml

@@ -379,6 +379,16 @@ jobs:
       - run: CC=gcc-10 CXX=g++-10 V=1 SKIP_LINK=1 ROCKSDB_CXX_STANDARD=c++20 make -j16 all | .circleci/cat_ignore_eagain # Linking broken because libgflags compiled with newer ABI
       - post-steps
 
+  build-linux-gcc-11-no_test_run:
+    machine:
+      image: ubuntu-2004:202010-01
+    resource_class: xlarge
+    steps:
+      - pre-steps
+      - run: sudo apt-get update -y && sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test && sudo apt-get install gcc-11 g++-11 libgflags-dev
+      - run: CC=gcc-11 CXX=g++-11 V=1 SKIP_LINK=1 make -j16 all | .circleci/cat_ignore_eagain # Linking broken because libgflags compiled with newer ABI
+      - post-steps
+
   # This job is only to make sure the microbench tests are able to run, the benchmark result is not meaningful as the CI host is changing.
   build-linux-microbench:
     machine:
@@ -779,6 +789,7 @@ workflows:
       - build-linux-gcc-8-no_test_run
       - build-linux-gcc-9-no_test_run
       - build-linux-gcc-10-cxx20-no_test_run
+      - build-linux-gcc-11-no_test_run
       - build-linux-arm-cmake-no_test_run
   build-macos:
     jobs:

table/table_test.cc

@@ -1365,7 +1365,7 @@ TEST_F(TablePropertyTest, PrefixScanTest) {
                                 {"num.555.3", "3"}, };
 
   // prefixes that exist
-  for (const std::string& prefix : {"num.111", "num.333", "num.555"}) {
+  for (const std::string prefix : {"num.111", "num.333", "num.555"}) {
     int num = 0;
     for (auto pos = props.lower_bound(prefix);
          pos != props.end() &&
@@ -1380,7 +1380,7 @@ TEST_F(TablePropertyTest, PrefixScanTest) {
   }
 
   // prefixes that don't exist
-  for (const std::string& prefix :
+  for (const std::string prefix :
        {"num.000", "num.222", "num.444", "num.666"}) {
     auto pos = props.lower_bound(prefix);
     ASSERT_TRUE(pos == props.end() ||