Currently, the following valid compiler directive file:
```
[{
  match: "*::*",
  c2: { Exclude: true } // c1 only for startup
}]
```
will be rejected by the parser:
```
Syntax error on line 4 byte 2: Expected value separator or object end (one of ',}').
  At ']'.
}]

Parsing of compiler directives failed
```

This is because `JSON::skip_line_comment()`, in contradiction to its specification, does **not** "*return the first token after the line comment without consuming it*" but does consumes it.

The fix is trivial:
```
--- a/src/hotspot/share/utilities/json.cpp
+++ b/src/hotspot/share/utilities/json.cpp
@@ -580,7 +580,7 @@ u_char JSON::skip_line_comment() {
     return 0;
   }
   next();
- return next();
+ return peek();
 }
```