[BUG] Support unqualified btr, bts


I happened to notice that linux.git uses plenty of btr and bts
instructions (not btrl, btrw, btsl, btsw). For examples, see
arch/x86/include/asm/bitops.h. LLVM barfs on these due to ambiguity,
while GNU as is fine with them. Surely, there must be architectures
where the w/l variant is unavailable? LLVM must support those
architectures, no?


Both variants have existed since the Intel 386.

That said, we should probably handle this like GNU as because the
variants behave almost identically. Please file a bug.


I don't consider this a bug. Just like certain FP instructions, they
*are* ambigious and there is no reason to depend on magic assembler