build: Allow each arch to manage include files

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
arch/um: Copy results of uname()

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
arch/un: Do not use host includes in non arch specific code

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
arch/um: Add basic interrupt support

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>