os/support: implement atomic_*() using GCC builtin helpers

If GCC knows what these functions are actually doing the resulting
code can be optimized better what is especially noticeable in case of
invocations of atomic_{or,and}() that ignore the result. Obviously,
everything is inlined what also improves performance.

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

kernel/x86: Inline atomic functions and memory barriers

os/support: implement atomic_*() using GCC builtin helpers

If GCC knows what these functions are actually doing the resulting
code can be optimized better what is especially noticeable in case of
invocations of atomic_{or,and}() that ignore the result. Obviously,
everything is inlined what also improves performance.

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

kernel/x86: Inline atomic functions and memory barriers