[clang] [llvm] [clang] Add support for the c2000 architecture (PR #125663)

[via cfe-commits]

SonicStark wrote:

Excited to see your nice work!!!

AFAIK all *TI extension keywords* may confuse clang frontend, and treating them as macros would result in strange behaviors, e.g.
```c
// DSP2833x_PieVect.h
typedef interrupt void(*PINT)(void);
```
So special keywords handling would be necessary...

See [SPRU514Z - TMS320C28x Optimizing C/C++ Compiler](https://www.ti.com/lit/ug/spru514z/spru514z.pdf):
> 6.5 Keywords
> The C28x C/C++ compiler supports all of the standard C89 keywords, including const, volatile, and register. It supports all of the standard C99 keywords, including inline and restrict. It supports all of the standard C11 keywords. It also supports TI extension keywords `__interrupt`, `__cregister`, and `__asm`.
> ...
>  6.5.2 The `__cregister` Keyword
> ...
>  6.5.3 The `__interrupt` Keyword
> ...

CMIIW :) @DragonDisciple

https://github.com/llvm/llvm-project/pull/125663