Use zend_string_equals() API instead of strcmp() in various places

Closes GH-6784

Author: Girgias

Zend/zend_compile.c

@@ -7902,7 +7902,7 @@ static bool zend_try_ct_eval_magic_const(zval *zv, zend_ast *ast) /* {{{ */
 			ZSTR_LEN(dirname) = zend_dirname(ZSTR_VAL(dirname), ZSTR_LEN(dirname));
 #endif
 
-			if (strcmp(ZSTR_VAL(dirname), ".") == 0) {
+			if (zend_string_equals_literal(dirname, ".")) {
 				dirname = zend_string_extend(dirname, MAXPATHLEN, 0);
 #if HAVE_GETCWD
 				ZEND_IGNORE_VALUE(VCWD_GETCWD(ZSTR_VAL(dirname), MAXPATHLEN));

ext/gd/gd.c

@@ -3182,7 +3182,7 @@ static void php_imagettftext_common(INTERNAL_FUNCTION_PARAMETERS, int mode)
 			if (key == NULL) {
 				continue;
 			}
-			if (strcmp("linespacing", ZSTR_VAL(key)) == 0) {
+			if (zend_string_equals_literal(key, "linespacing")) {
 				strex.flags |= gdFTEX_LINESPACE;
 				strex.linespacing = zval_get_double(item);
 			}

ext/standard/string.c

@@ -4634,7 +4634,7 @@ PHP_FUNCTION(strip_tags)
 static zend_string *try_setlocale_str(zend_long cat, zend_string *loc) {
 	const char *retval;
 
-	if (!strcmp("0", ZSTR_VAL(loc))) {
+	if (zend_string_equals_literal(loc, "0")) {
 		loc = NULL;
 	} else {
 		if (ZSTR_LEN(loc) >= 255) {

ext/xml/xml.c

@@ -813,7 +813,7 @@ void _xml_characterDataHandler(void *userData, const XML_Char *s, int len)
 
 					ZEND_HASH_REVERSE_FOREACH_VAL(Z_ARRVAL(parser->data), curtag) {
 						if ((mytype = zend_hash_str_find(Z_ARRVAL_P(curtag),"type", sizeof("type") - 1))) {
-							if (!strcmp(Z_STRVAL_P(mytype), "cdata")) {
+							if (zend_string_equals_literal(Z_STR_P(mytype), "cdata")) {
 								if ((myval = zend_hash_str_find(Z_ARRVAL_P(curtag), "value", sizeof("value") - 1))) {
 									int newlen = Z_STRLEN_P(myval) + ZSTR_LEN(decoded_value);
 									Z_STR_P(myval) = zend_string_extend(Z_STR_P(myval), newlen, 0);