Specify C++ language mode for warning post amdgpu-arch failure

Change-Id: I55bf6734a1e8dc06dd0a1ee12086b7667332206f

hipamd/hip-config-amd.cmake.in

@@ -103,7 +103,8 @@ if(NOT GPU_TARGETS)
 
         " As a result, --offload-arch will not be set for subsequent\n"
         " compilations, and the default architecture\n"
-        " (gfx906 for dynamic build / gfx942 for static build) will be used\n")
+        " (gfx906 for dynamic build / gfx942 for static build) will be used\n"
+        " for compiling device code in C++ language mode\n")
   else()
     # rocm_agent_enumerator adds gfx000 entry
     string(REPLACE "gfx000\n" "" AMDGPU_ARCH_OUTPUT "${AMDGPU_ARCH_OUTPUT}")