It is specific to C/C++, for sure -- I started with that. ccache is going to be as fast as any checksum dependency tracker --- otherwise you're relying on a ti

It is specific to C/C++, for sure -- I started with that. ccache is going to be as fast as any checksum dependency tracker --- otherwise you're relying on a timestamp, which isn't any better than "bare" Make. We use `*.d` rules from the `-MD` flag to prevent the "deleted header" case. Considering the brevity of the Makefile (it looks like a "basic" build), performance, and the practical robustness, it's in a pretty great trade-off space.