Print variables used in Dockerfile.spack_build

Being more verbose allows us to cross check values faster

.gitlab/docker/Dockerfile.spack_build

@@ -13,6 +13,7 @@ ARG CMAKE_FLAGS
 
 COPY . ${SOURCE_DIR}
 
+
 # Print spack spec since not printed if the compiler image is found on jfrog
 RUN spack -e pika_ci spec -lI
 
@@ -23,6 +24,7 @@ RUN spack -e pika_ci config add "config:flags:keep_werror:all" && \
     if [[ $COMPILER =~ clang ]]; then \
         export PATH="$(spack location --install-dir llvm)/bin:$PATH"; \
     fi && \
+    echo "build_type: ${BUILD_TYPE}  cmake_flags: ${CMAKE_COMMON_FLAGS} ${CMAKE_FLAGS}" && \
     spack -e pika_ci build-env $spack_spec -- \
     bash -c " \
     cmake -B${BUILD_DIR} ${SOURCE_DIR} -DCMAKE_BUILD_TYPE=$BUILD_TYPE $CMAKE_COMMON_FLAGS $CMAKE_FLAGS && \