Support RocksDB shared library and new unique_ptr DB::Open API

Some distributions (e.g. Fedora) ship only a shared RocksDB that exports
RocksDB::rocksdb-shared rather than RocksDB::rocksdb. The CMake target
selection now falls back to the shared target when the static one is absent.

Newer RocksDB also changed DB::Open and DB::OpenForReadOnly to take
std::unique_ptr<DB>* instead of DB**. IfcFile.cpp uses SFINAE tag dispatch
to build against both old and new APIs without version detection.

src/ifcparse/IfcFile.cpp

@@ -7,6 +7,8 @@
 #endif
 
 #include <fstream>
+#include <memory>
+#include <utility>
 #include <sys/types.h>
 #include <sys/stat.h>
 
@@ -410,6 +412,26 @@ IfcUtil::IfcBaseClass* IfcParse::impl::rocks_db_file_storage::assert_existance(s
 }
 
 namespace {
+#ifdef IFOPSH_WITH_ROCKSDB
+    // Newer RocksDB releases (e.g. the one shipped by Fedora rawhide) changed
+    // DB::Open / DB::OpenForReadOnly to take a std::unique_ptr<DB>* and removed
+    // the raw DB** overloads. These helpers select whichever signature the
+    // installed RocksDB exposes, so the code builds against both old and new
+    // headers. The int/long tag prefers the unique_ptr form when both exist.
+    template <typename Fn>
+    auto rocksdb_open(Fn&& open, rocksdb::DB*& db, int)
+        -> decltype(open(std::declval<std::unique_ptr<rocksdb::DB>*>())) {
+        std::unique_ptr<rocksdb::DB> owned;
+        auto status = open(&owned);
+        db = owned.release();
+        return status;
+    }
+    template <typename Fn>
+    auto rocksdb_open(Fn&& open, rocksdb::DB*& db, long)
+        -> decltype(open(std::declval<rocksdb::DB**>())) {
+        return open(&db);
+    }
+#endif
     rocksdb::DB* init_db(const std::string& filepath, bool readonly) {
         rocksdb::DB* db = nullptr;
 #ifdef IFOPSH_WITH_ROCKSDB
@@ -446,9 +468,13 @@ namespace {
 
         rocksdb::Status status;
         if (readonly) {
-            status = rocksdb::DB::OpenForReadOnly(options, filepath, &db);
+            status = rocksdb_open([&](auto* dbptr) -> decltype(rocksdb::DB::OpenForReadOnly(options, filepath, dbptr)) {
+                return rocksdb::DB::OpenForReadOnly(options, filepath, dbptr);
+            }, db, 0);
         } else {
-            status = rocksdb::DB::Open(options, filepath, &db);
+            status = rocksdb_open([&](auto* dbptr) -> decltype(rocksdb::DB::Open(options, filepath, dbptr)) {
+                return rocksdb::DB::Open(options, filepath, dbptr);
+            }, db, 0);
         }
         if (!status.ok()) {
             return nullptr;