Support 1 and 2 byte cmpset on x86

[markj]

Summary

This is intended for use in the LinuxKPI - the DRM code needs it.

[kib]

sys/i386/include/atomic.h

222

There is %zN construct, which prints opcode suffix for operand N. I think it is supported by clang. If you use it, you would avoid passing the instruction mnemonic to macros. Also, I suspect that it would work without suffix at all.

[markj]

sys/i386/include/atomic.h

222

With clang 4.0 I get "error: invalid operand in inline asm," though it works with gcc 4.9. But indeed, it looks like the suffixes aren't needed anyway.

[markj]

Don't specify the operand type, it can be inferred.