Originally this was introduced in 055e646b ('coreutils: Guard against compiler not supporting __builtin_stpncpy_chk') four years ago. Right now this doesn't seem to serve any purpose and it conflicts with the hardening flags:
<command line>:2:9: warning: '_FORTIFY_SOURCE' macro redefined [-Wmacro-redefined]
#define _FORTIFY_SOURCE 2
^
<command line>:1:9: note: previous definition is here
#define _FORTIFY_SOURCE 0
^
1 warning generated.
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