Comment # 4 on bug 1170376 from Guillaume GARDET

(In reply to Aaron Puchert from comment #2)
> (In reply to Guillaume GARDET from comment #0)
> > 2) Add '-moutline-atomics' to the list of ignored flags in LLVM
> 
> (In reply to Dirk Mueller from comment #1)
> > It seems like 2) is the only option.
> 
> Wouldn't be the first time we're doing this so it's fine for me. [1]
> 
> Another option would be to remove it manually in the affected packages, I
> think there are few packages that build with Clang. But it's probably not a
> bad idea to go with 2) either way so that Clang supports our default flags.

So, going with 2) seems to be ok for everyone!

> Silly question: why can this behavior not be achieved with -mtune=armv8.1-a?

AFAIK, '-mtune=armv8.1-a' does not exist, and '-march=armv8.1-a' would break
all armv8.0 hardware as it will use instructions only available on v8.1,
including LSE atomics.
'-moutline-atomics' will make use of new LSE instructions only if hardware
support it, and will fallback to legacy instructions if hardware does not
support the new ones.

@Aaron, would you take care of the patches or should I prepare a SR?