Check exception after undef var notice

For simple assignments, we may not emit an exception check elsewhere,
so perform it directly after the undef var notice.

Author: nikic

ext/opcache/jit/zend_jit_x86.dasc

@@ -5896,6 +5896,8 @@ static int zend_jit_simple_assign(dasm_State    **Dst,
 			ZEND_ASSERT(Z_MODE(val_addr) == IS_MEM_ZVAL && Z_REG(val_addr) == ZREG_FP);
 			|	mov FCARG1d, Z_OFFSET(val_addr)
 			|	EXT_CALL zend_jit_undefined_op_helper, r0
+			|	test r0, r0
+			|	jz ->exception_handler_undef
 			if (save_r1) {
 				|	mov FCARG1a, aword T1 // restore
 			}

ext/opcache/tests/jit/assign_043.phpt

@@ -0,0 +1,22 @@
+--TEST--
+JIT ASSIGN: Undef var notice promoted to exception
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.file_update_protection=0
+opcache.jit_buffer_size=1M
+opcache.protect_memory=1
+--FILE--
+<?php
+set_error_handler(function($_, $m) {
+    throw new Exception($m);
+});
+try {
+    $a = $b;
+    NOT_REACHED;
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+Undefined variable $b