LibC: fix bsearch for large arrays

[tryfinally]

fix bsearch for large arrays due to index computation overflow and mixed signed/unsigned operations.

[awesomekling]

Please use commit messages to explain what you are changing and why.
From contribution guidelines:

Don't:
Use weasel-words like "refactor" or "fix" to avoid explaining what's being changed.

[BenWiederhake]

Awesome!

Is there a way to make bsearch a simple wrapper around AK::binary_search? This way, we would avoid having to fix the same bugs in several places, like it happened now with 615ba0f and your commit ^^

[tryfinally]

I will into it. I think refactoring both methods to use same core.