fix ldb_cmd_test.cc build with nondefault -DROCKSDB_NAMESPACE

[ajkr]

I landed #12159 which had the below compiler error when using -DROCKSDB_NAMESPACE, which broke the CircleCI "build-linux-static_lib-alt_namespace-status_checked" job:

tools/ldb_cmd_test.cc:1213:21: error: 'rocksdb' does not name a type
 1213 |   int Compare(const rocksdb::Slice& a, const rocksdb::Slice& b) const override {
      |                     ^~~~~~~
tools/ldb_cmd_test.cc:1213:35: error: expected unqualified-id before '&' token
 1213 |   int Compare(const rocksdb::Slice& a, const rocksdb::Slice& b) const override {
      |                                   ^
tools/ldb_cmd_test.cc:1213:35: error: expected ')' before '&' token
 1213 |   int Compare(const rocksdb::Slice& a, const rocksdb::Slice& b) const override {
      |              ~                    ^
      |                                   )
tools/ldb_cmd_test.cc:1213:35: error: expected ';' at end of member declaration
 1213 |   int Compare(const rocksdb::Slice& a, const rocksdb::Slice& b) const override {
      |                                   ^
      |                                    ;
tools/ldb_cmd_test.cc:1213:37: error: 'a' does not name a type
 1213 |   int Compare(const rocksdb::Slice& a, const rocksdb::Slice& b) const override {
      |                                     ^
...

Test Plan:

$ make clean && make OPT="-DROCKSDB_NAMESPACE=alternative_rocksdb_ns" ldb_cmd_test -j56

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@ajkr has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[pdillinger]

Thanks!

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@ajkr merged this pull request in 15487b8.