Make sure -DDLIB__CMAKE_GENERATED_A_CONFIG_H_FILE is propagated to nvcc so that

the odr violation checks don't erroneously trigger.

dlib/CMakeLists.txt

@@ -601,6 +601,9 @@ if (NOT TARGET dlib)
             # linux).
             list(APPEND CUDA_NVCC_FLAGS "-arch=sm_30;-D__STRICT_ANSI__;-D_MWAITXINTRIN_H_INCLUDED;-D_FORCE_INLINES;${FLAGS_FOR_NVCC}")
             list(APPEND CUDA_NVCC_FLAGS ${active_preprocessor_switches})
+            if (NOT DLIB_IN_PROJECT_BUILD)
+               LIST(APPEND CUDA_NVCC_FLAGS -DDLIB__CMAKE_GENERATED_A_CONFIG_H_FILE)
+            endif()
             if (NOT MSVC)
                list(APPEND CUDA_NVCC_FLAGS "-std=c++11")
             endif()