matching ${TZDIR} setting for, //absl/time/internal/cctz:zoneinfo.
This eliminates any hidden dependency on /usr/share/zoneinfo, and
enables the upcoming deletion of the embedded internal/zoneinfo.inc
data from //absl/time:test_util.
PiperOrigin-RevId: 488372848
Change-Id: If1c8525b5ca4348cb2fc3b4760819f791b6e9725
