build: default to Berkeley DB for 32 bit and ARM

CMakeLists.txt

@@ -218,8 +218,17 @@ if (DATABASE STREQUAL "lmdb")
 		endif()
 	  endif()
   endif()
+
+  if (BERKELEY_DB AND (ARCH_WIDTH STREQUAL "32" OR ARM6 OR ARM7))
+    message(STATUS "Using Berkeley DB as default DB type")
+    add_definitions("-DDEFAULT_DB_TYPE=\"berkeley\"")
+  else()
+    message(STATUS "Using LMDB as default DB type")
+    add_definitions("-DDEFAULT_DB_TYPE=\"lmdb\"")
+  endif()
 elseif (DATABASE STREQUAL "memory")
   set(BLOCKCHAIN_DB DB_MEMORY)
+  add_definitions("-DDEFAULT_DB_TYPE=\"memory\"")
 else()
   die("Invalid database type: ${DATABASE}")
 endif()

src/daemon/command_line_args.h

@@ -73,7 +73,7 @@ namespace daemon_args
   const command_line::arg_descriptor<std::string> arg_db_type = {
     "db-type"
   , "Specify database type"
-  , "lmdb"
+  , DEFAULT_DB_TYPE
   };
   const command_line::arg_descriptor<uint64_t> arg_prep_blocks_threads = {
     "prep-blocks-threads"