Implement variable and constant pinning

This is basically free.

Author: iluuu1994

Zend/tests/pattern_matching/is/pinning.phpt

@@ -0,0 +1,41 @@
+--TEST--
+Pinning pattern
+--FILE--
+<?php
+
+$a = 1;
+$b = '1';
+$c = 'foo';
+
+var_dump(1 is ^$a);
+var_dump(2 is ^$a);
+var_dump(1 is ^$b);
+var_dump('foo' is ^$c);
+var_dump('bar' is ^$c);
+var_dump('1' is ^$a);
+
+const A = 1;
+const B = '1';
+const C = 'foo';
+
+var_dump(1 is ^A);
+var_dump(2 is ^A);
+var_dump(1 is ^B);
+var_dump('foo' is ^C);
+var_dump('bar' is ^C);
+var_dump('1' is ^A);
+
+?>
+--EXPECT--
+bool(true)
+bool(false)
+bool(false)
+bool(true)
+bool(false)
+bool(false)
+bool(true)
+bool(false)
+bool(false)
+bool(true)
+bool(false)
+bool(false)

Zend/zend_language_parser.y

@@ -1412,6 +1412,8 @@ pattern:
 
 atomic_pattern:
 		scalar_pattern { $$ = zend_ast_create(ZEND_AST_EXPR_LIKE_PATTERN, $1); }
+	|	'^' T_VARIABLE { $$ = zend_ast_create(ZEND_AST_EXPR_LIKE_PATTERN, zend_ast_create(ZEND_AST_VAR, $2)); }
+	|	'^' constant { $$ = zend_ast_create(ZEND_AST_EXPR_LIKE_PATTERN, $2); }
 	|	type_pattern { $$ = $1; }
 	|	object_pattern { $$ = $1; }
 	|	array_pattern { $$ = $1; }