The comments indicated that setting a Makefile variable USE_NSEC would
enable the code for sub-second [cm]times. However, the Makefile
variable was never turned into a compiler switch so the code was never
enabled. This patch allows USE_NSEC to be noticed by the compiler.
Signed-off-by: Brian Gernhardt <benji@silverinsanity.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>