[clang] [clang][bytecode] Fix unknown size arrays crash in clang bytecode (PR #160015)

[Timm Baeder via cfe-commits]

================
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -std=c++20 -fexperimental-new-constant-interpreter %s -verify
+// RUN: %clang_cc1 -std=c++20 %s -verify=ref
+
+// expected-no-diagnostics
+// ref-no-diagnostics
+
----------------
tbaederr wrote:

```suggestion

/// Test that __builtin_strlen() on external/unknown declarations doesn't crash the bytecode interpreter.

extern const char s[];

void foo(char *x)
{
    unsigned long len = __builtin_strlen(s);
    __builtin_strcpy(x, s);
}
```

https://github.com/llvm/llvm-project/pull/160015