use raw string for regex in `pre_configure_hook_cmake_system` #378

Job	Run time
eessi_container_script (run)	2m 20s
eessi_container_script (container)	4m 1s
eessi_container_script (shell)	3m 31s
eessi_container_script (resume)	4m 37s
eessi_container_script (help)	3m 13s
eessi_container_script (listrepos_custom)	2m 48s
eessi_container_script (listrepos_default)	3m 31s
eessi_container_script (unionfs)	7m 37s
	31m 38s

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