[clang] [Hexagon] Fix B0 macro conflict between hexagon_types.h and termios.h (PR #184539)

[Brian Cain via cfe-commits]

androm3da wrote:

> I'm fine with this change. Not sure if there's a better fix available for this. This change will guard the function definition but the call sites for B0 will not work. Should consider renaming the function too?

Yeah - this solution is not as effective as I thought.  Renaming should work, I'll do that instead.

https://github.com/llvm/llvm-project/pull/184539