kernel: panic() and assert() dump messages to stdout
lib: s/format/fmt/g
lib/macros: Make return_if_fail() verbose
arch/x86: Fix return_if_fail() regression

If tty_putc() fails, it calls return_if_fail(), which in turn calls
tty_putc(). This breaks the infinite loop by instead having the tty
subsystem fail silently.
init: Fix subsystems boolean logic