RFR: 8220632: Suggest recompiling with a larger value of -Xmaxerrs/-Xmaxwarns if diagnostics were suppressed

[Liam Miller-Cushon]

This change adds notes if diagnostics were suppressed due to the current
value of -Xmaxerrs/-Xmaxwarns, e.g.:

```
3 more warnings not shown; consider recompiling with -Xmaxwarns 100 to see
them
```

bug: https://bugs.openjdk.java.net/browse/JDK-8220632
webrev: http://cr.openjdk.java.net/~cushon/8220632/webrev.00/
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