Split `run_compiler` so users can get the location of the compiler?

[jlapeyre]

I want to use PackageCompiler for a completely different project that involves compiling C code. It would be useful if I could just find the compiler. You could rewrite run_compiler like this:

function run_compiler(cmd::Cmd; cplusplus::Bool=false)
    compiler_cmd = find_compiler_cmd(cplusplus)
    full_cmd = `$compiler_cmd $cmd`
    @debug "running $full_cmd"
    run(full_cmd) 
end

And put the rest of the existing function body in find_compiler_cmd instead. Then we could call find_compiler_cmd for other projects.

As it is, we can still just call run_compiler. But, if the function were split as suggested here, we'd have more flexibility, and options for debugging and handling exceptional situations.

This might help resolving #714 . For example, you could call find_compiler_cmd before trying to build your project.

[DilumAluthge]

Closed by #731

[DilumAluthge]

#731 introduced get_compiler_cmd, which is equivalent to the hypothetical find_compiler_cmd function in the OP.