GCC 10 and GCC 9.3.1+ support '-moutline-atomics' [0], so we could enable this
flag in Tumbleweed to improve LSE atomic operations on armv8.1+ hardware, with
very small overhead for armv8.0 hardware.

The problem is llvm does not support this flag and returns an error if used:
  clang-10.0: error: unknown argument: '-moutline-atomics'

The problem is optflags in Tumbleweed PrjConf targets both GCC and LLVM, so
adding '-moutline-atomics' would break LLVM builds.
I can see few solutions:
1) Enable '-moutline-atomics' by default in GCC packages [1]
2) Add '-moutline-atomics' to the list of ignored flags in LLVM
3) Split optflags to optflags_common, optflags_gcc and optflags_llvm

[0]: https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html#AArch64-Options
[1]: https://gcc.gnu.org/legacy-ml/gcc-patches/2019-09/msg01035.html