That file is specially compiled using a different set of flags. This is done deliberately, and is not an issue. You can squelch the false positive using an appropriate stanza in debian/rules, to issue a command in the log that tells blhc to stand down. Like this:
execute_before_dh_auto_build:
@echo "blhc: ignore-line-regexp: .*/CMakeCXXCompilerABI.cpp.*"
