[clang] [CIR][CIRGen] Upstream support for `__builtin_bcopy` (PR #185038)

[Ayokunle Amodu via cfe-commits]

ayokunle321 wrote:

@andykaylor for some reason, when i tired to add this [test](https://github.com/llvm/clangir/blob/63412d47b3d573ba2d7d55920541269930d4a303/clang/test/CIR/CodeGen/builtin-bcopy.cpp#L34-L49) it crashed with `Assertion failed: (mightHaveTerminator()), function getTerminator, file Block.cpp, line 250`. Any clue as to why? It's similar to the other tests.

I thought it had to do with the funky return but I tried this 

```mlir
void test_conditional_bcopy(void) {
  char dst[20];
  char src[20];
  int _sz = 20, len = 20;
  
  if (_sz)
    (_sz >= len) ? __builtin_bcopy(src, dst, len) : foo();
  else
    __builtin_bcopy(src, dst, len);
}
```
and it still crashed.

And should this be reviewed and merged first before making an issue about the crash? Or it should be sorted out in this PR?

https://github.com/llvm/llvm-project/pull/185038