Refactor InitPostgres() to use bitwise option flags

InitPostgres() has been using a set of boolean arguments to control its
behavior, and a patch under discussion was aiming at expanding it with a
third one.  In preparation for expanding this area, this commit switches
all the current boolean arguments of this routine to a single bits32
argument instead.  Two values are currently supported for the flags:
- INIT_PG_LOAD_SESSION_LIBS to load [session|local]_preload_libraries at
startup.
- INIT_PG_OVERRIDE_ALLOW_CONNS to allow connection to a database even if
it has !datallowconn.  This is used by bgworkers.

Reviewed-by: Bertrand Drouvot
Discussion: https://postgr.es/m/ZSTn66_BXRZCeaqS@paquier.xyz

src/backend/utils/init/postinit.c

@@ -681,8 +681,9 @@ BaseInit(void)
  * Parameters:
  *	in_dbname, dboid: specify database to connect to, as described below
  *	username, useroid: specify role to connect as, as described below
- *	load_session_libraries: TRUE to honor [session|local]_preload_libraries
- *	override_allow_connections: TRUE to connect despite !datallowconn
+ *	flags:
+ *	  - INIT_PG_LOAD_SESSION_LIBS to honor [session|local]_preload_libraries.
+ *	  - INIT_PG_OVERRIDE_ALLOW_CONNS to connect despite !datallowconn.
  *	out_dbname: optional output parameter, see below; pass NULL if not used
  *
  * The database can be specified by name, using the in_dbname parameter, or by
@@ -701,8 +702,8 @@ BaseInit(void)
  * database but not a username; conversely, a physical walsender specifies
  * username but not database.
  *
- * By convention, load_session_libraries should be passed as true in
- * "interactive" sessions (including standalone backends), but false in
+ * By convention, INIT_PG_LOAD_SESSION_LIBS should be passed in "flags" in
+ * "interactive" sessions (including standalone backends), but not in
  * background processes such as autovacuum.  Note in particular that it
  * shouldn't be true in parallel worker processes; those have another
  * mechanism for replicating their leader's set of loaded libraries.
@@ -717,8 +718,7 @@ BaseInit(void)
 void
 InitPostgres(const char *in_dbname, Oid dboid,
 			 const char *username, Oid useroid,
-			 bool load_session_libraries,
-			 bool override_allow_connections,
+			 bits32 flags,
 			 char *out_dbname)
 {
 	bool		bootstrap = IsBootstrapProcessingMode();
@@ -1189,7 +1189,8 @@ InitPostgres(const char *in_dbname, Oid dboid,
 	 * user is a superuser, so the above stuff has to happen first.)
 	 */
 	if (!bootstrap)
-		CheckMyDatabase(dbname, am_superuser, override_allow_connections);
+		CheckMyDatabase(dbname, am_superuser,
+						(flags & INIT_PG_OVERRIDE_ALLOW_CONNS) != 0);
 
 	/*
 	 * Now process any command-line switches and any additional GUC variable
@@ -1227,7 +1228,7 @@ InitPostgres(const char *in_dbname, Oid dboid,
 	 * during the initial transaction in case anything that requires database
 	 * access needs to be done.
 	 */
-	if (load_session_libraries)
+	if ((flags & INIT_PG_LOAD_SESSION_LIBS) != 0)
 		process_session_preload_libraries();
 
 	/* report this backend in the PgBackendStatus array */