[clang] [Clang] Amend SME attributes with support for ZT0. (PR #77941)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

The additional size of ExtProtoInfo and FunctionType  are both, IMO, problematic, we should be shrinking these.

>This also make me wonder if we should be reserving some extra bits for future state that may need adding?

The point is to minimize the size of these, since adding additional bits like this is limiting the code we can compile.  The 'extra bits' were an attempt to organize, not to minimize the size.

Why is the spec that this is from being so aggressive about modifying the types of functions?  This is causing some pretty annoying amounts of memory pressure in the compiler.  

IMO, we need to find some way to no longer store this information on the function type in a way that punishes every function.

https://github.com/llvm/llvm-project/pull/77941