[BUG] Support missing macro arguments

Hi,

I noticed that a macro defined like:

  .macro PTREGSCALL label, func, arg

is being called without the third argument like:

  PTREGSCALL stub32_rt_sigreturn, sys32_rt_sigreturn

GNU as supports this fine, but LLVM barfs (excerpt taken from
linux.git arch/x86/ia32/ia32entry.S). So it should perhaps be demoted
to a warning?

Thanks.