Fix HIP-Clang GPU build issues (#384)

* Fix HIP-Clang GPU build issues

Add missing device attributes for GPU functions. GPU functions must be annotated with __device__ in HIP.

* Use HIP device function max and min

* Fix clang-format-5.0 issues

* Undo change that breaks on HIP-HCC
Co-authored-by: mvermeulen <5479696+mvermeulen@users.noreply.github.com>

src/targets/gpu/device/sqrt.cpp

@@ -9,7 +9,7 @@ namespace device {
 
 void sqrt(hipStream_t stream, const argument& result, const argument& arg)
 {
-    nary(stream, result, arg)([](auto x) { return ::sqrt(to_hip_type(x)); });
+    nary(stream, result, arg)([](auto x) __device__ { return ::sqrt(to_hip_type(x)); });
 }
 
 } // namespace device

src/targets/gpu/device/sub.cpp

@@ -8,7 +8,7 @@ namespace device {
 
 void sub(hipStream_t stream, const argument& result, const argument& arg1, const argument& arg2)
 {
-    nary(stream, result, arg1, arg2)([](auto x, auto y) { return x - y; });
+    nary(stream, result, arg1, arg2)([](auto x, auto y) __device__ { return x - y; });
 }
 
 } // namespace device

src/targets/gpu/device/tan.cpp

@@ -9,7 +9,7 @@ namespace device {
 
 void tan(hipStream_t stream, const argument& result, const argument& arg)
 {
-    nary(stream, result, arg)([](auto x) { return ::tan(to_hip_type(x)); });
+    nary(stream, result, arg)([](auto x) __device__ { return ::tan(to_hip_type(x)); });
 }
 
 } // namespace device

src/targets/gpu/device/tanh.cpp

@@ -9,7 +9,7 @@ namespace device {
 
 void tanh(hipStream_t stream, const argument& result, const argument& arg)
 {
-    nary(stream, result, arg)([](auto x) { return ::tanh(to_hip_type(x)); });
+    nary(stream, result, arg)([](auto x) __device__ { return ::tanh(to_hip_type(x)); });
 }
 
 } // namespace device