Ada was designed for cross-language development. It was ahead of the curve on that. I'd be surprised if it was hard to integrate C today. The others I recall off top of head that went big in industry were OpenVMS (standard calling conventions, etc) and .NET CLR. I can't find my original article on "mixed, language development" in Ada but the marketing piece below gives you an idea of what developers were doing in 2005. Mixed language development, debugging, and traces. It's probably better now.

https://www.rti.com/hubfs/docs/2005Q1_2.pdf