devel/linux_libusb: disable date/time nonreproducible build warning

The base system build infrastructure will add -Wdate-time, to avoid
use of nonreproducible DATE and TIME in the base system.

This port makes use of a GCC that does not support -Wdate-time, so
opt out of the warning.

Reviewed by: hselasky
Approved by: jrm
PR: 267902 [exp-run]
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D37506