[HIP] Fix comdat of template kernel handle (#66283)

Currently, clang emits LLVM IR that fails verifier for the following
code:

```
template<typename T>
__global__ void foo(T x);

void bar() {
  foo<<<1, 1>>>(0);
}
```
This is due to clang putting the kernel handle for foo into comdat,
which is not allowed, since the kernel handle is a declaration.

The siutation is similar to calling a declaration-only template
function. The callee will be a declaration in LLVM IR and won't be put
into comdat. This is in contrast to calling a template function with
body, which will be put into comdat.

Fixes: SWDEV-419769