Allow initdb to complete on systems without "locale" command

This partially reverts 2fe3bdbd69, which
added an error check on the "locale -a" execution.  This is removed
again, adding a comment explaining why.  We already had code that
shows a warning if no system locales could be found, which should be
sufficient for feedback to the user.

Discussion: https://www.postgresql.org/message-id/flat/b2b491d1-3b36-15b9-6910-5b5540b27f5c%40enterprisedb.com

src/backend/commands/collationcmds.c

@@ -640,7 +640,6 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 		int			naliases,
 					maxaliases,
 					i;
-		int			pclose_rc;
 
 		/* expansible array of aliases */
 		maxaliases = 100;
@@ -747,15 +746,13 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 			}
 		}
 
-		pclose_rc = ClosePipeStream(locale_a_handle);
-		if (pclose_rc != 0)
-		{
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not execute command \"%s\": %s",
-							"locale -a",
-							wait_result_to_str(pclose_rc))));
-		}
+		/*
+		 * We don't check the return value of this, because we want to support
+		 * the case where there "locale" command does not exist.  (This is
+		 * unusual but can happen on minimalized Linux distributions, for
+		 * example.)  We will warn below if no locales could be found.
+		 */
+		ClosePipeStream(locale_a_handle);
 
 		/*
 		 * Before processing the aliases, sort them by locale name.  The point