[CUDA][HIP] warn incompatible redeclare (#77359)

nvcc warns about the following code:

`void f();
__device__ void f() {}`

but clang does not since clang allows device function to overload host
function.

Users want clang to emit similar warning to help code to be compatible
with nvcc.

Since this may cause regression with existing code, the warning is off
by default and can be enabled by -Wnvcc-compat.

It won't cause warning in system headers, even with -Wnvcc-compat.