Description:
------------
When an expression such as `(2)::class` (with brackets) is parsed in source code, PHP (debug and non-debug) crashes.

Debug builds emit this failure: "/path/to/php-src/Zend/zend_ast.h:298: zend_ast_get_str: Assertion `zval_get_type(&(*(zv))) == 6' failed."

This may also affect stable php versions. I also saw this in a recent PHP 7.4 build.

Non-debug builds segfault:

Program received signal SIGSEGV, Segmentation fault.
0x00000000009b5e19 in zend_get_class_fetch_type ()
(gdb) bt
#0  0x00000000009b5e19 in zend_get_class_fetch_type ()
#1  0x00000000009b62e0 in zend_try_compile_const_expr_resolve_class_name.part ()
#2  0x00000000009bcc5a in zend_compile_class_const ()
#3  0x00000000009bd255 in zend_compile_expr ()
#4  0x00000000009be6ab in zend_compile_echo ()
#5  0x00000000009c55e8 in zend_compile_stmt ()
#6  0x00000000009c972a in zend_compile_top_stmt ()
#7  0x00000000009c977f in zend_compile_top_stmt ()
#8  0x00000000009c977f in zend_compile_top_stmt ()
#9  0x000000000099c3dd in zend_compile ()
#10 0x000000000099dfb8 in compile_string ()
#11 0x00000000009cd00b in zend_eval_stringl ()
#12 0x00000000007e6967 in readline_shell_run ()
#13 0x0000000000a822c5 in do_cli ()
#14 0x000000000045f56c in main ()


Test script:
---------------
<?php
if (false) {
    echo (2)::class;
}

Expected result:
----------------
Should not segfault. Instead, it should emit a similar error to what PHP already does in other cases

```
php > echo []::class;
Fatal error: Dynamic class names are not allowed in compile-time ::class fetch in php shell code on line 1
```