kernel/{arm, x86, x86_64}: improve context switching

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
kernel/arm: strex and ldrex offset must be 0

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
build: get coloured output from gcc

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