When we use libmetal with other headers using stdatomic.h, we'll get
symbol conflict if we don't enable HAVE_STDATOMIC_H in libmetal. The
best solution might be using cmake to detect headers automatically, but
we can't. Fortunately we have CONFIG_HAVE_ATOMICS macro now, which can
replace HAVE_STDATOMIC_H when we're not using cmake.
Note: 2-Steps to use CONFIG_HAVE_ATOMICS
1. Include compiler.h for CONFIG_HAVE_ATOMICS definition
2. Check CONFIG_HAVE_ATOMICS instead of HAVE_STDATOMIC_H
Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
