Ignore `'<string>'` filepath (#17330)

Signed-off-by: rzou <zou3519@gmail.com>

vllm/compilation/backends.py

@@ -382,6 +382,10 @@ class VllmBackend:
             hash_content = []
             for filepath in forward_code_files:
                 hash_content.append(filepath)
+                if filepath == "<string>":
+                    # This means the function was dynamically generated, with
+                    # e.g. exec(). We can't actually check these.
+                    continue
                 with open(filepath) as f:
                     hash_content.append(f.read())
             import hashlib