[clang] [llvm] [Hexagon] Set the default compilation target to V68 (PR #125239)

[Brian Cain via cfe-commits]

androm3da wrote:

> I opened a SuperOps ticket SUPEROPS-12973 to update the 21.0 release notes.

That is for the downstream toolchain in the Hexagon SDK.  The upstream `llvm-project/clang/docs/ReleaseNotes.rst` needs to change.

Also: I don't think that the downstream toolchain will experience any change, so it's likely not needed to include it in those release notes.

https://github.com/llvm/llvm-project/pull/125239