Create c style math function ltgm query

[kevingranade]

Summary

SUMMARY: None

Purpose of change

There have been perennial problems caused by invoking c-style match functions such as floor() and exp() instead of the equivalent c++ style functions such as std::floor() and std::exp().
Most recently they triggered a large number of lgtm.com warnings (just noise) due to the fact that the c-style variants do not have float overloads while the c++ style equivalents do.

Describe the solution

Add this query to mark new instances of these functions to discourage their proliferation.

Describe alternatives you've considered

The listing is incomplete, the full list of functions is quite extensve, see cppreference.com, I'll add more later.

Testing

Let lgtm do its thing.

Additional context

I'm interested to see what over checks we can use this for, it seems very flexible and easy to use.
See https://lgtm.com/help/lgtm/writing-custom-queries for the outline of adding them.