Two non-functional changes:
- Remove pointless `-latomic` flag. It was specified via
`add_compile_options`, which only affects compilation and not linking,
so the library was never actually linked into the kernel. In fact, we
do not even build `libatomic` for our toolchain.
- Do not disable `-Wnonnull`. The warning-causing code was fixed at some
point.
This commit also removes `-mstrict-align` from the userland. Our target
AArch64 hardware natively supports unaligned accesses without a
significant performance penalty. Allowing the compiler to insert
unaligned accesses into aligned-as-written code allows for some
performance optimizations in fact. We keep this option turned on in the
kernel to preserve correctness for MMIO, as that might be sensitive to
alignment.