Reduce duplicated warnings for the change of Ruby 3 keyword arguments

By this change, the following code prints only one warning.

```
def foo(**opt); end
100.times { foo({kw:1}) }
```

A global variable `st_table *caller_to_callees` is a map from caller to
a set of callee methods.  It remembers that a warning is already printed
for each pair of caller and callee.

[Feature #16289]

0 files changed, 0 insertions, 0 deletions