fixes to build CUDA with Clang (#2681)

Author: BenWibking

Src/Base/AMReX_GpuUtility.H

@@ -27,7 +27,7 @@ namespace Gpu {
     AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
     T LDG (Array4<T> const& a, int i, int j, int k) noexcept {
 #ifdef __CUDA_ARCH__
-        return __ldg(a.ptr(i,j,k,n));
+        return __ldg(a.ptr(i,j,k));
 #else
         return a(i,j,k);
 #endif

Src/Base/AMReX_TypeTraits.H

@@ -81,7 +81,7 @@ namespace amrex
     template <class T, class Enable = void>
     struct DefinitelyNotHostRunnable : std::false_type {};
 
-#if defined(AMREX_USE_CUDA)
+#if defined(AMREX_USE_CUDA) && defined(__NVCC__)
 
     template <class T>
     struct MaybeHostDeviceRunnable<T, std::enable_if_t<__nv_is_extended_device_lambda_closure_type(T)> >