Parse split arguments from compile_commands.json

Current [`compile_commands.json` parser](https://github.com/w0rp/ale/blob/d476578a402763f2c6e4e0ada2eb345d0ac938d7/autoload/ale/c.vim#L176) only parses from the `command` string property. Using [Bear](https://github.com/rizsotto/Bear) to generate my `compile_commands.json` I instead have an `arguments` array of arguments, which is [an alternative supported by the JSON Compilation Database format](https://clang.llvm.org/docs/JSONCompilationDatabase.html#format).

Also of note, my compile command is using split `-I some/path` arguments rather than `-Isome/path`. A quick hack of `join(l:item.arguments, ' ')` resulted in an invocation like `clang [...] "-I/absolute/path some/path"`, I think the single string command parser also needs to be enhanced to correctly parse split arguments.

I may find some time to work on this in the next couple of weeks if no-one else does.