[clang] [Clang] Fix incorrect handling of #pragma {GCC} unroll N in dependent context (PR #90240)

[via cfe-commits]

yronglin wrote:

I have question, for the case `#pragma unroll {0|1}`, which AST attribute node make sense?

1.
```
LoopHintAttr 0x14b0bae08 <line:12:13, col:32> Implicit unroll Unroll Disable
```
or

2.
```
LoopHintAttr 0x15780a408 <line:12:13, col:32> Implicit unroll UnrollCount Numeric
```
Do we need accurate AST or real semantics here?

https://github.com/llvm/llvm-project/pull/90240