Fix hashing for codegenProc (sic) types

Since the name mangling is inhibited we should take the user-supplied
name during the sighash computation.

Fixes #8964

tests/ccgbugs/t8964.nim

@@ -0,0 +1,10 @@
+discard """
+  targets: "c cpp"
+"""
+
+from json import JsonParsingError
+import marshal
+
+const nothing = ""
+doAssertRaises(JsonParsingError):
+  var bar = marshal.to[int](nothing)