Automatically determine C/C++ compiler from build files

Because we now have a generic `cc` linter as of #3299, and the default executable setting is now `''` for C and C++ compilers, we can go one step further and automatically determine the C/C++ compiler to use from `compile_commands.json` or `make -n` output, etc. This will mean that ALE can automatically use the same C/C++ compiler that will be run when you run `make` by default, supposing you haven't told ALE to run some other compiler, as long as you either turn on the unsafe `make -n` parsing, or have a `compile_commands.json` file available that ALE can read.