Code Modernization: Replace substr( PHP_OS, 0, 3 ) calls with `PHP_…

…OS_FAMILY`.

The `PHP_OS_FAMILY` constant indicates the operating system family PHP was built for, and is available as of PHP 7.2.0.

Reference: [https://www.php.net/manual/en/reserved.constants.php#constant.php-os-family PHP Manual: Predefined Constants: PHP_OS_FAMILY].

Follow-up to [23255], [57753], [57985], [58678].

Props ayeshrajans, jrf.
See #61574.

git-svn-id: https://develop.svn.wordpress.org/trunk@58684 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -2257,11 +2257,11 @@ function get_temp_dir() {
  * @return bool Whether the path is writable.
  */
 function wp_is_writable( $path ) {
-	if ( 'WIN' === strtoupper( substr( PHP_OS, 0, 3 ) ) ) {
+	if ( 'Windows' === PHP_OS_FAMILY ) {
 		return win_is_writable( $path );
-	} else {
-		return @is_writable( $path );
 	}
+
+	return @is_writable( $path );
 }
 
 /**

tests/phpunit/tests/filesystem/wpFilesystemDirect/base.php

@@ -160,7 +160,7 @@ public function create_file_if_needed( $path, $contents = '' ) {
 	 * @return bool Whether the operating system is Windows.
 	 */
 	public static function is_windows() {
-		return 'WIN' === substr( PHP_OS, 0, 3 );
+		return 'Windows' === PHP_OS_FAMILY;
 	}
 
 	/**