Merge bitcoin/bitcoin#29315: refactor: Compile unreachable walletdb code

fa3373d refactor: Compile unreachable code (MarcoFalke)

Pull request description:

  When unreachable code isn't compiled, compile failures are not detected.

  Fix this by leaving it unreachable, but compiling it.

  Fixes bitcoin/bitcoin#28999 (comment)

ACKs for top commit:
  achow101:
    ACK fa3373d
  ryanofsky:
    Code review ACK fa3373d. This looks good, and should prevent code in the else blocks from accidentally breaking.

Tree-SHA512: 3a3764915dfc935bf5d7a48f1ca151dcbac340c1cbdce8236b24ae9b4f04d6ee9771ed058ca60bcbca6e19d13671de3517f828a8f7ab6444c7cc4e3538d1ba4e

Author: achow101

src/wallet/walletdb.cpp

@@ -1498,20 +1498,26 @@ std::unique_ptr<WalletDatabase> MakeDatabase(const fs::path& path, const Databas
 
     if (format == DatabaseFormat::SQLITE) {
 #ifdef USE_SQLITE
-        return MakeSQLiteDatabase(path, options, status, error);
-#else
-        error = Untranslated(strprintf("Failed to open database path '%s'. Build does not support SQLite database format.", fs::PathToString(path)));
-        status = DatabaseStatus::FAILED_BAD_FORMAT;
-        return nullptr;
+        if constexpr (true) {
+            return MakeSQLiteDatabase(path, options, status, error);
+        } else
 #endif
+        {
+            error = Untranslated(strprintf("Failed to open database path '%s'. Build does not support SQLite database format.", fs::PathToString(path)));
+            status = DatabaseStatus::FAILED_BAD_FORMAT;
+            return nullptr;
+        }
     }
 
 #ifdef USE_BDB
-    return MakeBerkeleyDatabase(path, options, status, error);
-#else
-    error = Untranslated(strprintf("Failed to open database path '%s'. Build does not support Berkeley DB database format.", fs::PathToString(path)));
-    status = DatabaseStatus::FAILED_BAD_FORMAT;
-    return nullptr;
+    if constexpr (true) {
+        return MakeBerkeleyDatabase(path, options, status, error);
+    } else
 #endif
+    {
+        error = Untranslated(strprintf("Failed to open database path '%s'. Build does not support Berkeley DB database format.", fs::PathToString(path)));
+        status = DatabaseStatus::FAILED_BAD_FORMAT;
+        return nullptr;
+    }
 }
 } // namespace wallet