augment cmake library search path to include the CUDA stubs library folder

this will help configuring and compiling LAMMPS with CUDA support on
machines where there is no CUDA driver installed

cmake/Modules/Packages/GPU.cmake

@@ -30,7 +30,15 @@ file(GLOB GPU_LIB_SOURCES ${LAMMPS_LIB_SOURCE_DIR}/gpu/[^.]*.cpp)
 file(MAKE_DIRECTORY ${LAMMPS_LIB_BINARY_DIR}/gpu)
 
 if(GPU_API STREQUAL "CUDA")
+  find_package(CUDA QUIET)
+  # augment search path for CUDA toolkit libraries to include the stub versions. Needed to find libcuda.so on machines without a CUDA driver installation
+  if(CUDA_FOUND)
+    set(CMAKE_LIBRARY_PATH "${CUDA_TOOLKIT_ROOT_DIR}/lib64/stubs;${CUDA_TOOLKIT_ROOT_DIR}/lib/stubs;${CUDA_TOOLKIT_ROOT_DIR}/lib64;${CUDA_TOOLKIT_ROOT_DIR}/lib;${CMAKE_LIBRARY_PATH}")
     find_package(CUDA REQUIRED)
+  else()
+    message(FATAL_ERROR "CUDA Toolkit not found")
+  endif()
+
   find_program(BIN2C bin2c)
   if(NOT BIN2C)
     message(FATAL_ERROR "Could not find bin2c, use -DBIN2C=/path/to/bin2c to help cmake finding it.")