d_localtime_r_needs_tzset isn't tested, breaking time.t

[moben]

time.t fails with

# Failed test 7 - changes to $ENV{TZ} respected at op/time.t line 62
op/time.t ......................................................... Failed 1/72 subtests

here because d_localtime_r_needs_tzset isn't tested by configure. If I define it manually the test passes. (This is on linux, glibc, amd64)

full log is here if needed: https://gist.github.com/moben/7ca323b2814ecaef78a823b0a5724909

[arsv]

That would be a runtime test, however 'define' seems to be the safe default value there.
"For portable code, tzset(3) should be called before localtime_r()" — localtime_r(3)

5192e4d

Looks like 'undef' actually works in most cases, that's why it went unnoticed.