Add functionality to our build system for architecture-specific code

[frogrammer9]

Right now when when using SETUP_EXECUTABLE and SETUP_LIBRARY they glob_recurse for all .c, .h and .S files. It would be nice if, for example, it ignored "arch" directory and automatically added source files from "arch/riscv" directory (for example).

[qbojj]

I think it would be the best to just provide explicit directory list to the SETUP_* and not do GLOB_RECURSE, but plain GLOB