_CS_V6_ENV and _CS_V7_ENV were both added in Issue 7 of the standard. Issue 6 did not have _CS_V6_ENV.
Right now they are empty. We'll see if more is needed in the future, but I doubt it.
48e07bd597 confstr(3): Add minimal support for V_ENV.
include/unistd.h | 2 ++
lib/libc/gen/confstr.c | 5 +++++
usr.bin/getconf/confstr.gperf | 2 ++
3 files changed, 9 insertions(+)