These should be builtins imo, LDC could reuse LLVM intrinsics and GDC could reuse GCC stuff, and DMD wich would reuse what ever is in ``core.atomics`` https://llvm.org/docs/Atomics.html#libcalls-atomic https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html