fix several bugs in the CI scripts

- use unbound variable LD_LIBRARY_PATH in install_cuda.sh
- use g++-12 in custom jobs, which is not available on Ubuntu 20.04

script/gitlabci/job_cuda.yml

@@ -1,26 +1,26 @@
 # SPDX-License-Identifier: MPL-2.0
 
 # nvcc + g++
-linux_nvcc12.0_gcc12_debug_relocatable_device_code_compile_only:
+linux_nvcc12.0_gcc11_debug_relocatable_device_code_compile_only:
   extends: .base_cuda_gcc_compile_only
   image: registry.hzdr.de/crp/alpaka-group-container/alpaka-ci-ubuntu20.04-cuda110-gcc:3.2
   variables:
     ALPAKA_CI_UBUNTU_VER: "20.04"
     ALPAKA_CI_CUDA_VERSION: "12.0"
-    ALPAKA_CI_GCC_VER: 12
+    ALPAKA_CI_GCC_VER: 11
     CMAKE_BUILD_TYPE: Debug
     ALPAKA_BOOST_VERSION: 1.81.0
     ALPAKA_CI_CMAKE_VER: 3.26.5
     alpaka_CXX_STANDARD: 17
     alpaka_RELOCATABLE_DEVICE_CODE: "ON"
 
-linux_nvcc12.0_gcc12_release_extended_lambda_off_compile_only:
+linux_nvcc12.0_gcc11_release_extended_lambda_off_compile_only:
   extends: .base_cuda_gcc_compile_only
   image: registry.hzdr.de/crp/alpaka-group-container/alpaka-ci-ubuntu20.04-cuda110-gcc:3.2
   variables:
     ALPAKA_CI_UBUNTU_VER: "20.04"
     ALPAKA_CI_CUDA_VERSION: "12.0"
-    ALPAKA_CI_GCC_VER: 12
+    ALPAKA_CI_GCC_VER: 11
     CMAKE_BUILD_TYPE: Release
     ALPAKA_BOOST_VERSION: 1.82.0
     ALPAKA_CI_CMAKE_VER: 3.27.1

script/install_cuda.sh

@@ -16,6 +16,11 @@ ALPAKA_CUDA_VER_SEMANTIC=( ${ALPAKA_CI_CUDA_VERSION//./ } )
 ALPAKA_CUDA_VER_MAJOR="${ALPAKA_CUDA_VER_SEMANTIC[0]}"
 echo ALPAKA_CUDA_VER_MAJOR: "${ALPAKA_CUDA_VER_MAJOR}"
 
+# if LD_LIBRARY_PATH is not set, the following statement will throw an unbound variable error
+# export LD_LIBRARY_PATH=/path/to/lib:${LD_LIBRARY_PATH} 
+if [ -z ${LD_LIBRARY_PATH+x} ]; then
+    export LD_LIBRARY_PATH=""
+fi
 
 if agc-manager -e cuda@${ALPAKA_CI_CUDA_VERSION}
 then