Re: change "microcode: Use fallthrough attribute on clang 10 and 11 too." broke the build for me

[Chris Hanson]

OK, we have to treat the Apple clang differently.

Prior to v12 no attribute is necessary as there are no warnings for 
falling through. Starting with v12 the usual attribute is required and 
works.

I'll make the change and cherry-pick to release-11, unless you want to 
do it.

On 2/14/21 2:10 PM, Taylor R Campbell wrote:
> > Date: Sun, 14 Feb 2021 21:24:56 +0000 (UTC)
> >
> > The problem appears to be between clang 11 and 12. In v11, the
> > attribute isn't recognized, and in v12 it is.
> >
> > Changing the conditional to __clang_major__ >= 12 fixes the problem
> > on macos.
> >
> > Taylor, why did you choose 10 instead?
> I verified that __attribute__((__fallthrough__)) works with clang
> 10.0.1 -- example program attached (fails with -Wimplicit-fallthrough
> -Werror, works if I uncomment the line).
>
> Not supporting the attribute seem to be a quirk of Apple's version of
> clang, from what I can tell.  What _does_ work in Apple's toolchain to
> selectively suppress -Wimplicit-fallthrough warnings?
>
>
> $ clang --version
> clang version 10.0.1
> Target: x86_64-unknown-netbsd9.0
> Thread model: posix
> InstalledDir: /pkg/2020Q3/bin