cuda : use std::string instead of VLA for archName (#30463)
* cuda : use std::string instead of VLA for archName
Modernize the code (old C style) and fix the following warnings:
```
ggml/src/ggml-cuda/ggml-cuda.cu:180:19: warning: variable length arrays in C++ are a Clang extension [-Wvla-cxx-extension]
180 | char archName[archLen + 1];
| ^~~~~~~~~~~
ggml/src/ggml-cuda/ggml-cuda.cu:180:19: note: read of non-const variable 'archLen' is not allowed in a constant expression
ggml/src/ggml-cuda/ggml-cuda.cu:179:9: note: declared here
179 | int archLen = strlen(devName);
| ^
```
Signed-off-by: Adrien Gallouët <angt@huggingface.co>
* Add a comment about archName
Signed-off-by: Adrien Gallouët <adrien@gallouet.fr>
---------
Signed-off-by: Adrien Gallouët <angt@huggingface.co>
Signed-off-by: Adrien Gallouët <adrien@gallouet.fr>