Support configurable WAL segment size.

PostgreSQL 11 introduces configurable WAL segment sizes, from 1MB to 1GB.

There are two areas that needed to be updated to support this: building the archive-get queue and checking that WAL has been archived after a backup.  Both operations require the WAL segment size to properly build a list.

Checking the archive after a backup is still implemented in Perl and has an active database connection, so just get the WAL segment size from the database.

The archive-get command does not have a connection to the database, so get the WAL segment size from pg_control instead.  This requires a deeper inspection of pg_control than has been done in the past, so it seemed best to copy the relevant data structures from each version of PostgreSQL and build a generic interface layer to address them.  While this approach is a bit verbose, it has the advantage of being relatively simple, and can easily be updated for new versions of PostgreSQL.

Since the integration tests generate pg_control files for testing, teach Perl how to generate files with the correct offsets for both 32-bit and 64-bit architectures.

test/lib/pgBackRestTest/Module/Mock/MockAllTest.pm

@@ -207,8 +207,10 @@ sub run
         # Create global path
         $oHostDbMaster->manifestPathCreate(\%oManifest, MANIFEST_TARGET_PGDATA, 'global');
 
-        $oHostDbMaster->manifestFileCreate(\%oManifest, MANIFEST_TARGET_PGDATA, DB_FILE_PGCONTROL, '[replaceme]',
-                                              'b4a3adade1e81ebfc7e9a27bca0887a347d81522', $lTime - 100, undef, true);
+        $oHostDbMaster->manifestFileCreate(
+            \%oManifest, MANIFEST_TARGET_PGDATA, DB_FILE_PGCONTROL, '[replaceme]',
+            $self->archBits() == 32 ? '8107e546c59c72a8c1818fc3610d7cc1e5623660' : '4c77c900f7af0d9ab13fa9982051a42e0b637f6c',
+            $lTime - 100, undef, true);
 
         # Copy pg_control
         $self->controlGenerate($oHostDbMaster->dbBasePath(), PG_VERSION_94);