[clang] [clang] Enable -fstack-clash-protection by default for Android (PR #209279)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

> > @shafik what was your goal cc'ing @MaskRay here? 🤔
> 
> I'm not Shafik but I can answer this. The [related RFC](https://discourse.llvm.org/t/rfc-enable-fstack-clash-protection-by-default-for-android-targets/91223/) came up for discussion at the Clang Area Team meeting yesterday. We noted that there was a prior RFC on the same topic but with a broader focus and it had push back from @MaskRay, but he hadn't weighed in on the new RFC. We wanted to ensure he saw the new RFC given his previous concerns, in case those concerns applied even in the more narrow case.

Muy goal was bring visibility to potentially concerned parties as per the clang area team discussion. 

I think Aaron's more general comments reflect my feeling as well. 

https://github.com/llvm/llvm-project/pull/209279