> The issue is that math.h includes cmath in gcc/clang which pulls in a lot of C++ machinery, and in C++17 in libstdc++ adds a slew of new special functions, that are rarely useful but will make compilation slower anyway.

> This is definitely an area where libstdc++ and libc++ could improve in the future - I don’t think it’s reasonable to force users of C headers to pay for the C++ baggage.